#include <bits/stdc++.h>
//十年OI一场空，不开long long见祖宗~
using namespace std;
typedef long long LL;

int main() {
    int n;
    cin >> n;
    LL a = 1, b = 1, c = 0;
    for (int i = 3; i <= n; i++) {
        c = a + b;
        a = b;
        b = c;
    }
    cout << c << ".00" << endl;
    return 0;
}