#include<bits/stdc++.h>

using namespace std;

typedef long long ll;

#define int long long

int Convert(int n)
{
	for (int w = 1; w < 1e10; w *= 10)
	{
		if (n / w % 10 == 4) n += w * 3;
		if (n / w % 10 == 7) n -= w * 3;
	}
	return n;
}

signed main()
{
	int A, B;
	cin >> A >> B;
	int a = Convert(A), b = Convert(B);
	printf("%lld\n", (a > b) ? A : B);
	return 0;
}