#include <bits/stdc++.h>
using namespace std;

#define _p(...) (void)printf(__VA_ARGS__)
#define forr(x,arr) for(auto&& x:arr)
#define _overload3(_1,_2,_3,name,...) name
#define _rep2(i,n) _rep3(i,0,n)
#define _rep3(i,a,b) for(int i=int(a);i<int(b);++i)
#define rep(...) _overload3(__VA_ARGS__,_rep3,_rep2,)(__VA_ARGS__)
#define _rrep2(i,n) _rrep3(i,0,n)
#define _rrep3(i,a,b) for(int i=int(b)-1;i>=int(a);i--)
#define rrep(...) _overload3(__VA_ARGS__,_rrep3,_rrep2,)(__VA_ARGS__)
#define ALL(x) (x).begin(), (x).end()
#define BIT(n) (1LL<<(n))
#define SZ(x) ((int)(x).size())
#define fst first
#define snd second
typedef vector<int> vi;typedef vector<vi> vvi;typedef pair<int,int> pii;typedef vector<pii> vpii;
typedef long long ll;

void Main() {
  string a, b;
  cin >> a >> b;
  if (SZ(a) != SZ(b)) {
    if (SZ(a) > SZ(b)) cout << a << endl;
    else cout << b << endl;
    return;
  }

  int n = SZ(a);
  rep(i, n) {
    int c = a[i] - '0';
    int d = b[i] - '0';
    if (c == d) continue;
    if (c == 4 && d == 7) cout << a << endl;
    else if (c == 7 && d == 4) cout << b << endl;
    else if (c > d) cout << a << endl;
    else cout << b << endl;
    return;
  }
}
int main() { cin.tie(0); ios::sync_with_stdio(false); Main(); return 0; }