#include <iostream>
using namespace std;

int main() {
    int dp[90] = {0}; //记录中间状态
    //店铺[i]表示到第i级台阶的方案数
    dp[1] = 1;
    dp[2] = 2;
    int n;
    scanf("%d", &n);
    for (int i = 3; i <= n; i++) {
        dp[i] = dp[i - 1] + dp[i - 2];
    }
    printf("%d\n", dp[n]);
    return 0;

}
// 64 位输出请用 printf("%lld")