#include <stdio.h>

int count(int n)
{
    return n > 2 ? count(n - 1) + count(n - 2) : n; 
}

int main()
{
    int n = 0;
    scanf("%d", &n);//输入
    int ret = count(n);//计算
    printf("%d\n", ret);//输出
    return 0;
}