#include<iostream>
#include<vector>

using namespace std;

typedef long long ll;

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

    return 0;
}