import java.util.*; import java.io.*; public class Main { public static void main(String[] args) { FastScanner sc = new FastScanner(); long a = sc.nextLong(); long b = sc.nextLong(); String sa = Long.toString(a); String sb = Long.toString(b); if (sa.length() > sb.length()) { System.out.println(sa); return; } else if (sa.length() < sb.length()) { System.out.println(sb); return; } for (int i = 0; i < sa.length(); i++) { if (sa.charAt(i) == '4' && sb.charAt(i) == '7') { System.out.println(sa); return; } if (sa.charAt(i) == '7' && sb.charAt(i) == '4') { System.out.println(sb); return; } if (sa.charAt(i) > sb.charAt(i)) { System.out.println(sa); return; } if (sa.charAt(i) < sb.charAt(i)) { System.out.println(sb); return; } } if (a > b) { System.out.println(sa); } else { System.out.println(sb); } } } class FastScanner { private final InputStream in = System.in; private final byte[] buffer = new byte[1024]; private int ptr = 0; private int buflen = 0; private boolean hasNextByte() { if (ptr < buflen) { return true; } else { ptr = 0; try { buflen = in.read(buffer); } catch (IOException e) { e.printStackTrace(); } if (buflen <= 0) { return false; } } return true; } private int readByte() { if (hasNextByte()) return buffer[ptr++]; else return -1; } private static boolean isPrintableChar(int c) { return 33 <= c && c <= 126; } public boolean hasNext() { while (hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++; return hasNextByte(); } public String next() { if (!hasNext()) throw new NoSuchElementException(); StringBuilder sb = new StringBuilder(); int b = readByte(); while (isPrintableChar(b)) { sb.appendCodePoint(b); b = readByte(); } return sb.toString(); } public long nextLong() { if (!hasNext()) throw new NoSuchElementException(); long n = 0; boolean minus = false; int b = readByte(); if (b == '-') { minus = true; b = readByte(); } if (b < '0' || '9' < b) { throw new NumberFormatException(); } while (true) { if ('0' <= b && b <= '9') { n *= 10; n += b - '0'; } else if (b == -1 || !isPrintableChar(b)) { return minus ? -n : n; } else { throw new NumberFormatException(); } b = readByte(); } } public int nextInt() { long nl = nextLong(); if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE) throw new NumberFormatException(); return (int) nl; } public double nextDouble() { return Double.parseDouble(next()); } }