#include <bits/stdc++.h>

using ll = long long;
using std::cin;
using std::cout;
using std::endl;

std::mt19937 rnd(std::chrono::steady_clock::now().time_since_epoch().count());
template <class T>
inline bool chmax(T &a, T b)
{
    if (a < b)
    {
        a = b;
        return 1;
    }
    return 0;
}
template <class T>
inline bool chmin(T &a, T b)
{
    if (a > b)
    {
        a = b;
        return 1;
    }
    return 0;
}

constexpr int inf = (int)1e9 + 7;
constexpr long long INF = 1LL << 60;

void solve()
{
    ll C, Y;
    cin >> C >> Y;
    std::vector<ll> coin = {1, 5, 10, 50, 100, 500, 1000, 2000, 5000, 10000};
    std::map<ll, ll> cnt;
    std::reverse(coin.begin(), coin.end());
    for (const auto &e : coin)
    {
        cnt[e] = Y / e;
        Y %= e;
    }
    if (cnt[100] >= C)
    {
        cout << "no exchange\n";
        return;
    }
    for (const auto &e : coin)
    {
        if (e <= 500)
            break;
        cnt[500] += (e / 500) * cnt[e];
    }
    if (cnt[500] * 5 + cnt[100] < C)
    {
        cout << "can't exchange\n";
    }
    else
    {
        ll req = (C - cnt[100]);
        cnt[100] += 5 * ((req + 4) / 5);
        cout << cnt[100] << "\n";
    }
}

int main()
{
    std::cin.tie(nullptr);
    std::ios_base::sync_with_stdio(false);
    int kkt = 1;
    // cin >> kkt;
    while (kkt--)
    {
        solve();
    }
}