#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define rrep(i,n) for(int i = 1; i <= (n); ++i)
#define drep(i,n) for(int i = (n)-1; i >= 0; --i)
#define srep(i,s,t) for (int i = s; i < t; ++i)
#define rng(a) a.begin(),a.end()
using namespace std;
typedef long long int ll;
typedef pair<int,int> P;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<ll> vl;
typedef vector<P> vp;
#define dame { puts("-1"); return 0;}
#define yn {puts("Yes");}else{puts("No");}
#define MAX_N 200005

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