Fibonacci

#include <bits/stdc++.h>
#define int long long

using namespace std;

ifstream fin("text.in");
ofstream fout("text.out");

int32_t main() {
    int N, a = 0, b = 1;
    fin >> N;
    if(N == 0) {
        fout << 0;
        return 0;
    }
    if(N == 1) {
        fout << 1;
        return 0;
    }
    for(int i = 2; i <= N; ++i) {
        int c = a + b;
        a = b;
        b = c;
    }
    fout << b;
}