// #pragma GCC optimize("O3,unroll-loops")
#include <bits/stdc++.h>
// #include <x86intrin.h>
using namespace std;
#if __cplusplus >= 202002L
using namespace numbers;
#endif



int main(){
	cin.tie(0)->sync_with_stdio(0);
	cin.exceptions(ios::badbit | ios::failbit);
	int obj, cur;
	cin >> obj >> cur;
	cur /= 100;
	if(cur % 5 >= obj){
		cout << "no exchange\n";
		return 0;
	}
	if(cur < obj){
		cout << "can't exchange\n";
		return 0;
	}
	cout << (obj - cur % 5 + 4) / 5 * 5 + cur % 5 << "\n";
	return 0;
}

/*

*/