#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define ALL(v) v.begin(),v.end()
typedef long long ll;
 
#include<bits/stdc++.h>
using namespace std;

int main(){
  ios::sync_with_stdio(false);
  std::cin.tie(nullptr);
  
  ll c,y;
  cin>>c>>y;
  
  y/=100;
  if(y%5>=c) cout<<"no exchange"<<endl;
  else{
    c-=(y%5);
    y-=y%5;
    y/=5;
    if((c+4)/5>y) cout<<"can't exchange"<<endl;
    else cout<<((c+4)/5)*5<<endl;
  }
    
  return 0;
}