#include<iostream>
#include<stdio.h>
using namespace std;
#define MAX_VAL 54
#define int long long


signed main(){
	int N,dp[MAX_VAL] = {1,1};
	
	scanf("%d", &N);
	
	for(int i = 0; i <= N; i++){
		dp[i+2] = dp[i+1] + dp[i];
	}
	
	printf("%lld\n", dp[N]);
	
	return 0;
}