#include <bits/stdc++.h>
#define rep(i, n) for(int i = 0; i < (int)(n); i++)
#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()
#define UNIQUE(v) v.erase( unique(v.begin(), v.end()), v.end() );
using namespace std;
using ll = long long;

ll dp[51];

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