input_line1 = raw_input()
input_line2 = raw_input()

input_line1 = input_line1.split()
input_line2 = input_line2.split()

if input_line1[1] < input_line2[1]:
    print input_line2[0]
elif input_line1[1] > input_line2[1]:
    print input_line1[0]
else:
    print -1