#include <bits/stdc++.h>
using namespace std;
#include <atcoder/all>
// #include <atcoder/modint>
// #include <atcoder/math>
// #include <atcoder/segtree>
// #include <atcoder/lazysegtree>
// #include <atcoder/dsu>
// #include <atcoder/scc>
using namespace atcoder;

// #pragma GCC target("avx2")
// #pragma GCC optimize("O3")
// #pragma GCC optimize("unroll-loops")

typedef long long int ll;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<ll,ll> pll;
typedef vector<ll> vll;
typedef vector<vll> vvll;
typedef vector<vvll> vvvll;
typedef vector<pll> vpll;
typedef vector<vpll> vvpll;
typedef vector<bool> vb;
typedef vector<vb> vvb;
typedef vector<double> vd;
typedef vector<vd> vvd;
typedef priority_queue<pll, vpll, function<bool(pll,pll)> > pqpll; 
typedef priority_queue<ll, vll, function<bool(pll,pll)> > pqll;
 
struct edge{ ll to, cost; edge(ll e_to,ll e_cost): to(e_to), cost(e_cost){} };
typedef vector<vector<edge>> Graph;
 
#define rep(i,a,n) for(ll i = a;i < n;i++)
#define rrep(i,a,n) for(ll i = n-1; i >= a;i--)
#define LINF (1LL << 60)
#define INF (1 << 30)
#define fs first
#define sc second
#define EPS (ld)1e-10
#define ALL(a) a.begin(), a.end()
#define tcheck(a) if((clock() - start)/(ld)CLOCKS_PER_SEC >= a) break
#define debug(s) cout << #s << endl
#define debugval(x) cout << #x" = " << x << endl
 
template<typename T> ll sz(vector<T> &pos){ return (ll)pos.size(); }
template<typename T> ll sz(priority_queue<T, vector<T> > &que) {return (ll)que.size(); }
template<typename T> ll sz(priority_queue<T, vector<T>, greater<T> > &que) {return (ll)que.size(); }
ll sz(string &s) {return (ll)s.size(); } 
 
template<typename T> void chmin(T &a, T b) { if(a > b) a = b; }
template<typename T> void chmax(T &a, T b) { if(a < b) a = b; }

// __int128_t gcd(__int128_t a, __int128_t b){ return ((!b) ? a : gcd(b,a%b)); } 
ll gcd(ll a,ll b){ return ((!b) ?a :gcd(b, a%b)); }
ll lcm(ll a,ll b){ return a / gcd(a,b) * b; }
ll dx[4] = {0,-1,0,1},dy[4] = {-1,0,1,0};
// ll dx[8] = {0,-1,-1,-1,0,1,1,1},dy[8] = {-1,-1,0,1,1,1,0,-1};
inline bool isinside(ll i,ll n){ return (i < n && i >= 0); }

int main(){
    ll c,y;
    cin >> c >> y;

    vll money = vll({10000,5000,2000,1000,500,100,50,10,5,1});
    vll cnt(sz(money));

    ll cntsum = 0;
    rep(i,0,sz(money)){
        cnt[i] = y/money[i];
        y %= money[i];

        cntsum += cnt[i] * (money[i]/100);
    }

    if(cntsum < c) cout << "can't exchange" << endl;
    else if(cnt[5] >= c) cout << "no exchange" << endl;
    else{
        ll rem = c-cnt[5];
        cout << cnt[5]+((rem+4)/5)*5 << endl;
    }
}