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

ll Fibo[91];

int main(){ios_base::sync_with_stdio(false); cout.tie(NULL); cin.tie(NULL);

Fibo[0] = 0LL;
Fibo[1] = 1LL;
Fibo[2] = 1LL;
for (int i = 3; i <= 90; ++i)
	Fibo[i] = Fibo[i-1]+Fibo[i-2];

int N;
cin >> N;
cout << Fibo[N] << '\n';

return 0;
}