C++ :

#include<iostream>
using namespace std;

void output(int h, int m)
{
	if (h < 10)
		cout << '0';
	cout << h << ':';
	if (m < 10)
		cout << '0';
	cout << m << endl;
}

int main()
{
	int h1, h2, m1, m2;
	char c;
	while (cin >> h1 >> c >> m1)
	{
		cin >> h2 >> c >> m2;
		m1 += 60 - m2;
		h1 += 23 - h2;
		if (m1 >= 60)
		{
			h1++;
			m1 -= 60;
		}
		if (h1 >= 24)
			h1 -= 24;
		output(h1, m1);
	}
	return 0;
}