// <24127121>
// <Nguyen Tien Thanh>
// <24C09>
//Bai 10
 
//Test case 1
//input: 60  80 
//Output:  20
 
//Test case 2
//Input: 70  100
//Output: 30
 
//Test case 3
//Input: 10  100
//Output: 90
#include <iostream>
using namespace std;
int main() {
	unsigned int previous, current;
	do {
		cin >> previous >> current;
		if (current > previous) {
			unsigned int used = current - previous;
			cout << " " << used << endl;
		}
		else {
			cout << "Ban da nhap sai, vui long nhap lai!" << endl;
		}
	} while (current <= previous);
	return 0;
}

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NjAgODA=

60 80