#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
using namespace std;

__int64 dp[1000];

int main()
{
    dp[1]=1;
    dp[2]=2;
    dp[3]=3;
    dp[4]=5;
    for(int i=5;i<=60;i++)
    {
        dp[i]=dp[i-1]+1+dp[i-3];
    }
    int n;
    while(~scanf("%d",&n))
    {
        printf("%I64d\n",dp[n]);
    }

    return 0;
}