#include <bits/stdc++.h>

using namespace std;
void fast_io() {
    ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
}

int main() {
    fast_io();
    int c, y;
    cin >> c >> y;
    y /= 100;
    if (y < c) {
        cout << "can't exchange" << endl;
        return 0;
    }
    if (y % 5 >= c) {
        cout << "no exchange" << endl;
        return 0;
    }
    int ans = (c - y % 5 + 4) / 5 * 5 + y % 5;
    cout << ans << endl;
}