#include "bits/stdc++.h"
using namespace std;
using ll = long long; using pii = pair<int, int>;
const int MOD = (int)1e9 + 7, INF = (1 << 27); const ll INFLL = (1LL << 55);
#define FOR(i,a,b) for(int (i)=(a);i<(int)(b);i++)
#define rep(i,n) FOR(i,0,n)
template<typename T, typename U> inline void chmax(T &x, U y) { if (x < y) x = y; }
template<typename T, typename U> inline void chmin(T &x, U y) { if (x > y) x = y; }

bool f(int x, int y) {
    if (x == 4 && y == 7 || x == 7 && y == 4) {
        swap(x, y);
    }
    return x > y;
}

int main() {
    string a, b; cin >> a >> b;
    if (a.size() != b.size()) {
        cout << (a.size() > b.size() ? a : b) << "\n";
        return 0;
    }

    string aa = a, bb = b;
    reverse(a.begin(), a.end());
    reverse(b.begin(), b.end());
    int x = stoi(a), y = stoi(b);
    while (x) {
        int b1 = x % 10, b2 = y % 10;
        x /= 10; y /= 10;
        if (b1 == b2) continue;
        cout << (f(b1, b2) ? aa : bb) << "\n";
        break;
    }

    return 0;
}