#include <bits/stdc++.h>
using namespace std;
#define all(v) (v).begin(),(v).end()
#define pb(a) push_back(a)
#define rep(i, n) for(int i=0;i<n;i++)
#define foa(e, v) for(auto&& e : v)
using ll = long long;
const ll MOD7 = 1000000007, MOD998 = 998244353, INF = (1LL << 60);
#define dout(a) cout<<fixed<<setprecision(10)<<a<<endl;

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    ll c, y;
    cin >> c >> y;
    ll now100 = y % 500;
    now100 /= 100;
    if(now100 >= c) {
        cout << "no exchange" << endl;
        return 0;
    }
    if(y / 100 < c) {
        cout << "can\'t exchange" << endl;
        return 0;
    }
    c -= now100;
    cout << ((c + 4) / 5) * 5 + now100 << endl;
    return 0 ; 
}