#include<iostream>
#include<vector>
#include<cassert>
using namespace std;
int main()
{
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int C,Y;
	cin>>C>>Y;
	if(Y/100<C)
	{
		cout<<"can't exchange"<<endl;
		return 0;
	}
	if(Y%500/100>=C)
	{
		cout<<"no exchange"<<endl;
		return 0;
	}
	Y-=C*100;
	cout<<C+Y%500/100<<"\n";
}