#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<n;i++)
using namespace std;
using ll =  long long ;
using P = pair<int,int> ;
const int INF = 1e9;
const int MOD = 1000000007;

int main(){
    int n;
    cin >> n;
    vector<ll> dp(n+1);
    dp[0] = 1;
    for(int i=1;i<=n;i++){
        if(i==1) dp[i] = dp[i-1];
        else dp[i] = dp[i-1] + dp[i-2];
    }
    cout << dp[n] << endl;
    return 0;
}