/* -*- coding: utf-8 -*-
 *
 * 2681.cc:  No.2681 ゲームセンターの両替 - yukicoder
 */

#include<cstdio>
#include<algorithm>
 
using namespace std;

/* constant */

const int K = 10;
const int xs[K] = { 1, 5, 10, 50, 100, 500, 1000, 2000, 5000, 10000 };

/* typedef */

/* global variables */

int cs[K];

/* subroutines */

/* main */

int main() {
  int c, y;
  scanf("%d%d", &c, &y);

  for (int i = K - 1; i >= 0; i--)
    cs[i] = y / xs[i], y %= xs[i];

  int r = c - cs[4];
  if (r <= 0) puts("no exchange");
  else {
    int sum = 0;
    for (int i = 5; i < K; i++) sum += cs[i] * xs[i];
    int maxr = ((sum / 100) / 5) * 5;

    if (r > maxr)
      puts("can't exchange");
    else
      printf("%d\n", (r + 4) / 5 * 5 + cs[4]);
  }

  return 0;
}