#include <iostream>
#include <cassert>
#include <vector>
#include <map>
#include <algorithm>

using namespace std;

int main() {
  vector<int> cands = {1,5,10,50,100,500};
  reverse(cands.begin(), cands.end());

  map<int, int> mp;
  int C, Y; cin >> C >> Y;
  for (int cand: cands) {
    int cnt = Y / cand;
    mp[cand] = cnt;
    Y -= cand * cnt;
  }

  if (mp[100] >= C) {
    cout << "no exchange" << endl;
  } else if (mp[500] * 5 + mp[100] < C) {
    cout << "can't exchange" << endl;
  } else {
    int need = C - mp[100];
    int t = ((need + 4) / 5);
    int ans = mp[100] + t * 5;
    cout << ans << endl;
  }
  return 0;
}