#include<iostream>
using namespace std;
#define FOR(i, a, n) for(int i=a; i<n; i++)

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

	long long dp[51];
	dp[0] = dp[1] = 1;
	FOR(i, 2, N + 1) dp[i] = dp[i - 1] + dp[i - 2];
	cout << dp[N] << endl;

    return 0;
}