#include <iostream>
#include <algorithm>
#include <vector>
#include <map>
#include <string>
#include <numeric>
#define rep(i,n) for(int i=0;i<(n);i++)

using ll = long long int;
using namespace std;

int main()
{
    int N;
    cin >> N;
    vector<ll> dp(N + 1);

    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;
}