Zadatak Kusac - honi-2013-2014-1

/*
    Zadatak: Kusac
             http://bit.ly/honi-2013-2014-1

    Datum: 2013-09-28

    Autor zadatka: HSIN/HONI

    Autor rješenja: Kristijan Burnik, udruga informaticara Božo Težak

    Gmail: kristijanburnik

*/
#include <iostream>

using namespace std;

int gcd(int a, int b) {
    if (b == 0)
       return a;
    else
       return gcd(b, a % b);
}

int main() {

    int n,m;

    cin >> n >> m;

    n %= m;

    if ( n % m == 0) {
        cout << 0;
    } else if (m % n == 0) {
        cout << m - n;
    } else {
        int g = gcd(n,m);
        n /= g; m /= g;

        cout << ( m / n ) * n;
    }

    cout << endl;

    // main();
    return 0;
}