import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines

A = readline().split()
B = readline().split()

PA = int(A[1])
PB = int(B[1])

if PA > PB:
    print(A[0].decode())
elif PA == PB:
    print(-1)
else:
    print(B[0].decode())