#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using ll = long long;
#define rep(i,n) for(ll i=0;i<(ll)(n);i++)
using mint = atcoder::modint998244353;

int main(){
	ll c,y;
	cin>>c>>y;
	if(c*100>y){
		cout<<"can't exchange\n";
		return 0;
	}
	ll nc=(y%500)/100;
	if(nc>=c){
		cout<<"no exchange\n";
		return 0;
	}
	cout<<((c-nc+4)/5)*5+nc<<endl;
}