// eddy1021
//#include <bits/stdc++.h>
#include <iostream>
#include <algorithm>
#include <math.h>
#include <stdlib.h>
#include <map>
#include <vector>
#include <queue>
#include <stdio.h>
#include <string.h>
using namespace std;
typedef double D;
typedef long long ll;
typedef pair<int,int> PII;
#define mod9 1000000009ll
#define mod7 1000000007ll
#define INF  1023456789ll
#define INF16 10000000000000000ll
#define FI first
#define SE second
#define PB push_back
#define MP make_pair
#define MT make_tuple
#define eps 1e-9
#define SZ(x) (int)(x).size()
ll getint(){
    ll _x=0,_tmp=1; char _tc=getchar();    
    while( (_tc<'0'||_tc>'9')&&_tc!='-' ) _tc=getchar();
    if( _tc == '-' ) _tc=getchar() , _tmp = -1;
    while(_tc>='0'&&_tc<='9') _x*=10,_x+=(_tc-'0'),_tc=getchar();
    return _x*_tmp;
}
ll mypow( ll _a , ll _x , ll _mod ){
    if( _x == 0 ) return 1ll;
    ll _tmp = mypow( _a , _x / 2 , _mod );
    _tmp = ( _tmp * _tmp ) % _mod;
    if( _x & 1 ) _tmp = ( _tmp * _a ) % _mod;
    return _tmp;
}
bool equal( D _x ,  D _y ){
    return _x > _y - eps && _x < _y + eps;
}
int __ = 1 , cs;
/*********default*********/
#define N 62
ll dp[ N ];
ll DP( int x ){
    if( x < 0 ) return 1;
    return dp[ x ];
}
void build(){
    dp[ 0 ] = 1;
    for( int i = 1 ; i < N ; i ++ ){
        dp[ i ] = dp[ i - 1 ];
        dp[ i ] += DP( i - 3 );
    }
}
int n;
void init(){

}
void solve(){
    cout << dp[ n ] - 1ll << endl;
}
int main(){
    build();
//    __ = getint();
//    while( __ -- ){
    while( cin >> n ){
        init();
        solve();
    }
}