#include <iostream>
#include <vector>
#include <algorithm>
#include <array>
#include <iterator>
#include <string>
#include <cctype>
#include <cstring>
#include <cstdlib>
#include <cassert>
#include <cmath>
#include <ctime>
#include <iomanip>
#include <numeric>
#include <stack>
#include <queue>
#include <map>
#include <unordered_map>
#include <set>
#include <unordered_set>
#include <bitset>
#include <random>
#include <utility>
#include <functional>
using namespace std;
void Main()
{
	int C,Y;
	cin >> C >> Y;
	const vector<int> A = {1,5,10,50,100,500,1000,2000,5000,10000};
	vector<int> cnt(A.size());
	int X = Y;
	for(int i = (int)A.size() - 1;i >= 0;i--)
	{
		cnt[i] = X / A[i];
		X %= A[i];
	}
	const int M = 100;
	if(cnt[4] >= C)
	{
		cout << "no exchange\n";
		return;
	}
	int all = 0;
	for(int i = 0;i < (int)A.size();i++)
	{
		all += A[i] / M * cnt[i];
	}
	if(all < C)
	{
		cout << "can't exchange\n";
	}
	else
	{
		//cnt[4] + 5 * x >= C
		//min(x) == ceil(C - cnt[4],5)
		cout << (C - cnt[4] + 4) / 5 * 5 + cnt[4] << "\n";
	}
}
int main()
{
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int tt = 1;
	/* cin >> tt; */
	while(tt--) Main();
}