#include <bits/stdc++.h>
using namespace std;
using ll = long long;

template<class T> istream& operator >> (istream& is, vector<T>& vec) {
    for(T& x : vec) is >> x;
    return is;
}

template<class T> ostream& operator << (ostream& os, const vector<T>& vec) {
    if(vec.empty()) return os;
    os << vec[0];
    for(auto it = vec.begin(); ++it != vec.end(); ) os << ' ' << *it;
    return os;
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    ll C, X;
    cin >> C >> X;
    vector<ll> a = {1,5,10,50,100,500,1000,2000,5000,10000};
    vector<ll> b(a.size());
    for(int i = a.size() - 1; i >= 0; i--){
        b[i] = X / a[i];
        X %= a[i];
    }
    if(b[4] >= C){
        cout << "no exchange" << '\n';
        return 0;
    }
    ll v = b[4];
    for(int i = 5; i < a.size(); i++){
        v += a[i] * b[i] / 100;
    }
    if(v < C){
        cout << "can't exchange\n";
    }else{
        v = (C - b[4] + 499) / 500;
        v = v * 5 + b[4];
        cout << v << '\n';
    }
}