#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;

#define rep(i,m) for(int i=0;i<n;i++)
typedef long long ll;

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