#include <iostream>
using namespace std;

int main() {
    int c, y;
    cin >> c >> y;
    int bc = (y % 1000) / 100;
    if (bc >= 5) {
        bc -= 5;
    }
    if (bc >= c) {
        cout << "no exchange" << endl;
    } else if (c * 100 > y) {
        cout << "can't exchange" << endl;
    } else {
        int rest = y - (100 * c);
        int b = (rest % 1000) / 100;
        if (b >= 5) {
            b -= 5;
        }
        cout << (b + c) << endl;
    }
    return 0;
}