#include <bits/stdc++.h>
#define rep(i,a,b) for(int i=a;i<b;i++)
#define rrep(i,a,b) for(int i=a;i>=b;i--)
using namespace std;
typedef long long ll;
typedef pair<int, int> P;
ll INF = 1e18;

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

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