//#include<bits/stdc++.h>
#define int long long
using namespace std;
int mem[100];
int dfs(int x)
{
	if(mem[x]) return mem[x];
	
	int sum = 0;
	if(x == 1) sum = 1;
	else if(x == 2) sum = 2;
	else sum = dfs (x - 1) + dfs(x - 2);
	
	mem[x] = sum;
	return sum;
}
signed main()
{
	int n;
	cin >> n;
	int res=dfs(n-1);
	cout << res << '\n';
	return 0;
//}