#include <bits/stdc++.h>
using namespace std;

#define rep(i, n) for (int i = 0; i < (int)(n); i++)

int main() {
  int C, Y;
  cin >> C >> Y;
  vector<int> yen = {1, 5, 10, 50, 100, 500, 1000, 2000, 5000, 10000};
  vector<int> coin(10, 0);
  int y = Y;
  rep(i, 10) {
    coin[(10-1) - i] = y / yen[(10-1) - i];
    y %= yen[(10-1) - i];
  }
  if (Y < C * 100)
    cout << "can't exchange" << endl;
  else if (coin[4] >= C)
    cout << "no exchange" << endl;
  else {
    int ret = coin[4];
    while (ret < C)
      ret += 5;
    cout << ret << endl;
  }
  return 0;
}