#include <cstdio>

long long sum[61];
long long dp[61];

int main() {
    dp[0]=0;
    dp[1]=dp[2]=dp[3]=1;
    sum[0]=0;
    sum[1]=1;
    sum[2]=2;
    sum[3]=3;
    for (int i=4;i<=60;i++) {
        dp[i]=sum[i-3]+1;
        sum[i]=sum[i-1]+dp[i];
    }
    int n;
    while (scanf("%d",&n)!=EOF) {
        printf("%I64d\n",sum[n]);
    }
    return 0;
}