#include <cstring>
#include <cmath>
#include <cstdio>
#include <climits>
#include <ctime>
#include <cassert>
#include <cctype>
#include <iostream>
#include <algorithm>
#include <numeric>
#include <map>
#include <set>
#include <queue>
#include <string>
#include <vector>
#include <bitset>
#include <utility>

#define all(x) (x).begin(), (x).end()
#define bit(x) (1 << (x))
#define cnt1(x) (__builtin_popcount(x))
#define LB lower_bound
#define LET(it,v) __typeof(v) it(v)
#define mset0(x) memset((x), 0, sizeof((x)))
#define mset1(x) memset((x), -1, sizeof((x)))
#define pb push_back
#define PQ priority_queue
#define REP(it,v) for(LET(it,v.begin());it!=v.end();it++)
#define sqr(x) ((x)*(x))
#define sz(x) ((int)(x.size()))
#define UB upper_bound
#define X first
#define Y second

using namespace std;
typedef long long LL;
typedef double DB;
typedef pair<int, int> pii;
typedef pair<LL, LL> pll;
typedef vector<int> vi;
typedef vector<pii> vpii;

template <class T> inline void chkmin(T &a, T b) {
    if (b < a) a = b;
}
template <class T> inline void chkmax(T &a, T b) {
    if (a < b) a = b;
}

const int MX = 3005;
vi con[MX];
pii e[MX];

int par[MX];
int chk[MX], CN;
int p[MX], pn;

void DFS(int u) {
    chk[u] = 1;
    for (int i = 0; i < sz(con[u]); i++) {
        pii tp = e[con[u][i]];
        int v = tp.X + tp.Y - u;
        if (!chk[v]) DFS(v);
    }
}

int vis[MX];
void DFS2(int u, int fe) {
    chk[u] = 1, par[u] = fe;
    for (int i = 0; i < sz(con[u]); i++) {
        if (con[u][i] == fe) continue;
        pii tp = e[con[u][i]];
        int v = tp.X + tp.Y - u;
        
        if (chk[v] && !vis[v]) {
            int tp = u;
            pn = 1, p[pn] = tp, chk[u] = 2;
            
            while (1) {
                tp = e[par[tp]].X + e[par[tp]].Y - tp;
                chk[tp] = 2, p[++pn] = tp;
                if (tp == v) break;
            }
        } else {
            chk[v] = 1;
            DFS2(v, con[u][i]);
        }
    }
    vis[u] = 1;
}

int sz[MX];
void DFS1(int u, int pr) {
    sz[u] = 0;
    for (int i = 0; i < sz(con[u]); i++) {
        pii tp = e[con[u][i]];
        int v = tp.X + tp.Y - u;
        if (chk[v] < CN && v != pr) {
            sz[u]++;
            DFS1(v, u);
        }
    }
}

bool can(int u, int pr, int fr) {
    int sz = 0;
    for (int i = 0; i < sz(con[u]); i++) {
        pii tp = e[con[u][i]];
        int v = tp.X + tp.Y - u;
        if (chk[v] < CN && v != pr) {
            sz++;
            if (!can(v, u, fr)) return 0;
        }
    }
    if (u != fr) return sz <= 1;
    return sz <= 2;
}

bool can1(int u, int pr) {
    int sz = 0;
    for (int i = 0; i < sz(con[u]); i++) {
        pii tp = e[con[u][i]];
        int v = tp.X + tp.Y - u;
        if (chk[v] < CN && v != pr) {
            sz++;
            if (!can1(v, u)) return 0;
        }
    }
    return sz <= 1;
}

int n, SS;
void in() {
    int i, j, u, v;
    for (i = 1; i <= n; i++) {
        chk[i] = 0;
        con[i].clear();
    }
    SS = -1;
    
    for (i = 1; i <= n; i++) {
        scanf("%d%d", &u, &v);
        if (u == v) {
            SS = u;
            continue;
        }
        e[i].X = u, e[i].Y = v;
        con[u].pb(i);
        con[v].pb(i);
    }
}

bool solve() {
    int i, j, u, v;
    
    DFS(1);
    for (i = 1; i <= n; i++) if (!chk[i]) return 0;
    CN = 2;
    
    if (SS != -1) {
        chk[SS] = 2;
        return can(SS, -1, SS);
    }
    
    mset0(chk);
    mset0(vis);
    DFS2(1, -1);
    
    int cnt = 0, flg1 = -1, flg2 = -1;
    for (j = 1; j <= pn; j++) {
        DFS1(p[j], -1);
        if (sz[p[j]]) {
            if (++cnt == 1) flg1 = j;
            else flg2 = j;
        }
    }
    if (cnt >= 3) return 0;
    if (cnt == 2) {
        if (flg2 != flg1 + 1 && (flg1 != 1 || flg2 != pn)) return 0;
    }
    
    int flg = 1;
    if (flg1 > 0) flg &= can1(p[flg1], -1);
    if (flg2 > 0) flg &= can1(p[flg2], -1);
    return flg;
}

int main() {
    
    while (scanf("%d", &n) == 1) {
        in();
        if (solve()) puts("YES");
        else puts("NO");
    }
    
    return 0;
}