#include<bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i,m,n) for(int i=m; i<n; ++i)
#define repl(i,m,n) for(ll i=m; i<n; ++i)

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

    vector<int> dp(N+1, 0);
    dp[0] = 1;

    rep(i, 0, N+1){
        if(i+1 <= N) dp[i+1] += dp[i];
        if(i+2 <= N) dp[i+2] += dp[i];
    }
    cout << dp.back() << endl;

    return 0;
}