#include <bits/stdc++.h>




namespace zawa {

using i16 = std::int16_t;
using i32 = std::int32_t;
using i64 = std::int64_t;
using i128 = __int128_t;

using u8 = std::uint8_t;
using u16 = std::uint16_t;
using u32 = std::uint32_t;
using u64 = std::uint64_t;

using usize = std::size_t;

} // namespace zawa


namespace zawa {

void SetFastIO() {
    std::cin.tie(nullptr)->sync_with_stdio(false);
}

void SetPrecision(u32 dig) {
    std::cout << std::fixed << std::setprecision(dig);
}

} // namespace zawa
using namespace zawa;

int val[11]{ 1, 5, 10, 50, 100, 500, 1000, 2000, 5000, 100000, (int)2e9 };
long long cnt[10];
int main() {
    SetFastIO();

    int c, y; std::cin >> c >> y;
    for (int i{} ; i < 10 ; i++) {
        cnt[i] = (y % (val[i + 1])) / val[i];
        y -= cnt[i] * val[i];
    }
    if (cnt[4] >= c) {
        std::cout << "no exchange " << '\n';
        return 0;
    }
    for (int i{9} ; i >= 6 ; i--) {
        cnt[5] += cnt[i] * (val[i] / 500);
    }
    long long all{cnt[5] * 5};
    if (all + cnt[4] < c) {
        std::cout << "can't exchange" << '\n';
        return 0;
    }
    long long need{(c - cnt[4] + 4) / 5};
    cnt[4] += need * 5;
    assert(need <= cnt[5]);
    std::cout << cnt[4] << '\n';
}