#include<bits/stdc++.h>
#define rep(i,a,n) for (int i = a; i < n; i++)
#define per(i,n,a) for (int i = n - 1; i >= a; i--)
using namespace std;

long long dp[100];
int main() {
    int n;
    cin >> n;
    dp[0] = dp[1] = 1;
    rep(i, 2, n + 1) {
        dp[i] = dp[i - 1] + dp[i - 2];
    }
    cout << dp[n] << endl;
}