#include<bits/stdc++.h>

using namespace std;

typedef long long ll;

#define int long long

signed main()
{
	int A, B;
	cin >> A >> B;
	int cA = A, cB = B;
	for (int w = 1; w < 1e10; w *= 10)
	{
		int a = A / w % 10, b = B / w % 10;
		int plusA = 0, plusB = 0;
		if (a == 4 && b == 7) plusA = 3, plusB = -3;
		if (a == 7 && b == 4) plusA = -3, plusB = 3;
		cA += w * plusA; cB += w * plusB;
	}
	printf("%lld\n", (cA > cB) ? A : B);
	return 0;
}