#include "bits/stdc++.h"
using namespace std;
#define ll long long int
#define rep(i,n) for( int i = 0; i < n; i++ )
#define rrep(i,n) for( int i = n; i >= 0; i-- )
#define REP(i,s,t) for( int i = s; i <= t; i++ )
#define RREP(i,s,t) for( int i = s; i >= t; i-- )
#define dump(x)  cerr << #x << " = " << (x) << endl;
#define INF 2000000000
#define mod 1000000007
#define INF2 1000000000000000000


int main(void)
{
	cin.tie(0);
	ios::sync_with_stdio(false);
	string A, B;
	cin >> A >> B;
	if (A.length() > B.length()) {
		cout << A << endl;
		return 0;
	}
	if (A.length() < B.length()) {
		cout << B << endl;
		return 0;
	}
	int R[10][10];
	rep(i, 10) {
		rep(j, 10) {
			if (i > j) R[i][j] = 1;
			else if(i == j) R[i][j] = 0;
			else  R[i][j] = -1;
		}
	}
	R[4][7] = 1;
	R[7][4] = -1;
	rep(i, A.length()) {
		int numA = A[i] - '0';
		int numB = B[i] - '0';
		if (R[numA][numB] == 0) continue;
		if (R[numA][numB] > 0) {
			cout << A << endl;
		}
		else {
			cout << B << endl;
		}
		return 0;
	}

    return 0;
}