import std;

void main() {
    long A, B;
    readf("%d %d\n", A, B);

    long N = A.to!real.log10.floor.to!long;
    long M = B.to!real.log10.floor.to!long;

    if (N > M) {
        A.writeln;
    }
    else if (N < M) {
        B.writeln;
    }
    else {
        long C = A, D = B;
        long E = 10 ^^ N;

        while (C > 0) {
            long c = C / E, d = D / E;

            if (c == 4 && d == 7) {
                A.writeln;
                break;
            }
            else if (c == 7 && d == 4) {
                B.writeln;
                break;
            }
            else {
                if (c > d) {
                    A.writeln;
                    break;
                }
                else if (c < d) {
                    B.writeln;
                    break;
                }
            }

            C %= E, D %= E;
            E /= 10;
        }
    }
}