#include using namespace std; using ll = long long; #define rep(i, n) for (int i = 0; i < (int)(n); i++) void solve() { ll c, y; cin >> c >> y; if (c * 100 > y) { cout << "can't exchange" << '\n'; return; } ll r = y % 500, d = c - r / 100; if (d <= 0) { cout << "no exchange" << '\n'; return; } cout << (d + 4) / 5 * 5 + r / 100 << '\n'; } int main() { std::cin.tie(nullptr); std::ios_base::sync_with_stdio(false); int T = 1; for (int t = 0; t < T; t++) { solve(); } return 0; }