#include<iostream>
#include<vector>
#include<set>
#include<map>
#include<list>
#include<stack>
#include<queue>
#include<bitset>
#include<array>
#include<algorithm>
#include<cstdio>
#include<string>
#include<cstdlib>
#include<numeric>
#define D			long long
#define U			unsigned
#define F(i,a)		for(i=0;i<a;i++)
#define bF(i,a)		for(i=1;i<=a;i++)
#define dF(i,a)		for(i=a-1;i>=0;i--)
#define bdF(i,a)	for(i=a;i>=1;i--)
#define LOCAL		D i=0,j=0,k=0,t=0,u=0
#define SIZE		1
using namespace std;
D n, m, a, b, d, e;
char c;
bool g, h;
string s;
D ans;
D p[SIZE];
int main() {
	LOCAL;
	cin >> a >> b;
	d = a;
	e = b;
	for (i = 1000000000; i > 0; i /= 10) {
		if ((a/i) % 10 == 4 && (b/i) % 10 == 7){
			a += i * 3;
			b -= i * 3;
		}
		else if ((a / i) % 10 == 7 && (b / i) % 10 == 4) {
			a -= i * 3;
			b += i * 3;
		}
	}
	if (a > b)
		cout << d << endl;
	else
		cout << e << endl;
}