#include <atcoder/all>
#include <bits/stdc++.h>
using ll = long long;
using ull = unsigned long long;
#define rep(i, n) for(int i = 0; i < (int)(n); i++)
#define REP(i, m, n) for(int i = (int)(m); i < (int)(n); i++)
using namespace std;
using namespace atcoder;
using mint = modint998244353;
const int inf = 1000000007;
const ll longinf = 1ll << 60;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    int c, y;
    cin >> c >> y;
    vector<int> v = {1, 5, 10, 50, 100, 500, 1000, 2000, 5000, 10000};
    vector<int> cnt(10);
    for(int i = 9; i >= 0; i--) {
        cnt[i] = y / v[i];
        y -= cnt[i] * v[i];
    }
    if(cnt[4] >= c) {
        cout << "no exchange" << endl;
        return 0;
    }
    int ma = 0;
    REP(i, 4, 10) {
        ma += cnt[i] * v[i] / 100;
    }
    if(ma < c) {
        cout << "can't exchange" << endl;
        return 0;
    }
    cout << (ma - c) % 5 + c << endl;
    return 0;
}