#include <iostream>

using i64 = long long;

int main() {
    i64 c, y;
    std::cin >> c >> y;
    if (y < c * 100ll) {
        std::cout << "can't exchange\n";
    } else {
        i64 c100 = (y % 500) / 100;
        if (c100 >= c) {
            std::cout << "no exchange\n";
        } else {
            std::cout << (c - c100 + 4) / 5 * 5 + c100 << "\n";
        }
    }

    return 0;
}