#include<iostream>
using namespace std;

int main(){
    int n;
    int F[50];
    cin >> n;
    F[0] = F[1] = 1;
    for(int i=2;i<=n;i++)F[i] = F[i-1] + F[i-2];

    cout << F[n] << endl;
    return 0;
}
