c_str = input().replace(" ","")
c_replace_1_list = list(map(int,c_str.replace("?","1")))
c_replace_4_list = list(map(int,c_str.replace("?","4")))
if c_replace_1_list[1] == min(c_replace_1_list) or c_replace_1_list[1] == max(c_replace_1_list):
    print(1,end = "")
if c_replace_4_list[1] == min(c_replace_4_list) or c_replace_4_list[1] == max(c_replace_4_list):
    print(4)