C++ :

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

int x, y;
char c;

int main() {
    cin >> x >> c >> y;

    // Find the greatest common divisor
    int a = x, b = y, t;
    while (b != 0) {
        t = a % b;
        a = b;
        b = t;
    }

    // Reduce the fraction
    cout << x / a << ":" << y / a << endl;

    return 0;
}