Strange and pointless algorithmic training

big_fib.cpp

#include <iostream>
using namespace std;

int main() {
    unsigned long long int fNum = 0;
    unsigned int div = 0;
    cin >> fNum >> div;
    //fNum = 11527523930876953;
    //div = 26673;

    unsigned int f1, f2, tmp;
    f1 = 0; f2 = 1;
    tmp = 0;

    int i = 0;
    while (true) {
        i++;
        tmp = f1;
        f1 = f2;
        f2 +=tmp;
        if (i == fNum) {
            cout << f1;
            return 0;
        }
        if (f2 >= div)
            break;
    }
//cout << "1\n";
    int i0 = ++i;
    tmp = f1;
    f1 = f2;
    f2 += tmp;
    f1 %= div; f2 %= div;

    unsigned int f10, f20;
    f10 = f1; f20 = f2;

    while (true) {
        i++;
        tmp = f1;
        f1 = f2;
        f2 += tmp;
        f1 %= div; f2 %= div;
        //if (f1 == 10552) cout << "yes!\n";
        if (f1 == f10 && f2 == f20)
            break;
    }
    //cout << "2\n";
    int t = i - i0;
    int n = (fNum - i0)%t;

    for(int j = 0; j < n; j++) {
        tmp = f1;
        f1 = f2;
        f2 += tmp;
        f1 %= div; f2 %= div;
        //cout << f1 << "\t" << f2 << "\n";
    }
    cout << f1;
    return 0;
}