#include <bits/stdc++.h>

#include <atcoder/all>
#define rep(i, a, b) for (ll i = (ll)(a); i < (ll)(b); i++)
using namespace std;
using namespace atcoder;

typedef long long ll;

int main() {
    int c, y;
    cin >> c >> y;
    int y10000, y5000, y1000, y500, y100;
    y10000 = y / 10000;
    y %= 10000;
    y5000 = y / 5000;
    y %= 5000;
    y1000 = y / 1000;
    y %= 1000;
    y500 = y / 500;
    y %= 500;
    y100 = y / 100;
    int nw = y100;
    int cnt = 0;
    while (nw < c) {
        cnt++;
        if (y10000) {
            y10000--;
            nw += 100;
            continue;
        }
        if (y5000) {
            y5000--;
            nw += 50;
            continue;
        }
        if (y1000) {
            y1000--;
            nw += 10;
            continue;
        }
        if (y500) {
            y500--;
            nw += 5;
            continue;
        }
        cout << "can't exchange" << endl;
        return 0;
    }
    if (cnt == 0) {
        cout << "no exchange" << endl;
        return 0;
    } else {
        int ans = y100;
        while (c > ans) ans += 5;
        cout << ans << endl;
    }
}