#include <iostream>
using namespace std;

int main(void){
    int n;
    cin >> n;
    long long dp[51];
    dp[0] = dp[1] = 1;
    for(int i=2; i<=n; i++){
        dp[i] = dp[i-1] + dp[i-2];
    }
    cout << dp[n] << endl;
    return 0;
}