#include<cstring>
#include<cstdio>
#include<algorithm>
#include<iostream>
#define rep(i,l,r) for (int i=l;i<=r;i++)
#define maxn 100050
#define inf 1152921504606846976
#define low(i) i&(-i)
#define clr(x,y) memset(x,y,sizeof(x))
#define ll long long
using namespace std;
int flag,n,sum[maxn],ss;
ll f[maxn],ans;
int read()
{
    int  x=0, f=1; char ch=getchar();
    while (!isdigit(ch)) {if (ch=='-') f=-1; ch=getchar();}
    while (isdigit(ch)) x=x*10+ch-'0', ch=getchar();
    return x*f;
}
int main(){
//    freopen("in.txt","r",stdin);
    while(~scanf("%d",&n)){
        ans=0;
        rep(i,1,n) f[i]=1;
        f[1]=f[2]=f[3]=1;
        rep(i,4,n)
            rep(j,1,i-3) f[i]+=f[j];
        rep(i,1,n)
            ans+=f[i];
        printf("%I64d\n",ans);    
    }
    return 0;
}