#include <iostream>
using namespace std;

using ll = long long;
#define FOR(i,a,b) for(int (i)=(a);i<(int)(b);i++)
#define rep(i,n) FOR(i,0,n)

int main() {
    int N;
    cin >> N;

    static ll dp[55] = {0};
    dp[0] = 1;
    rep(i, N) {
        dp[i + 1] += dp[i];
        dp[i + 2] += dp[i];
    }

    cout << dp[N] << endl;
    return 0;
}