#include<bits/stdc++.h>
using namespace std;

int n;
long long int memo[111];

long long int solve(int n){

	if(~memo[n]) return memo[n];
	if(n < 0) return 0;
	if(!n) return 1;
	
	return memo[n] = solve(n-1) + solve(n-2);
}

int main(){

	memset(memo, -1, sizeof(memo));
	cin >> n;
	cout << solve(n) << endl;
	
}