#include <iostream>
using namespace std;

int main() {
    int N; 
    cin >> N;
    int a = 1, b = 1, tmp;
    if (N != 1) {
        for (int i = 1; i < N; i++) {
            tmp = b;
            b = a + b;
            a = tmp;
        }
    }
    cout << b;
    
}
// 64 位输出请用 printf("%lld")

线性dp+状态压缩