#include <iostream>
using namespace std;
long long d[91];
int main() {
    int n;
    cin >> n;
    d[1] = 1;
    d[2] = 1;
    for (int i = 3; i <= n; i++) {
        d[i] = d[i - 1] + d[i-2];
    }
    cout << d[n] << endl;
    return 0;
}