f = open("text.txt", "r")
input = f.read()

matrix = [[.22,.22,.22,.33],[.22,.22,.22,.33],[.33,.33,.11,.22],[.22,.33,.11,.33],[.11,.22,.22,.44]]

probability = 0
output = ""
for i in range(0, len(input) -4):
    temp = 0
    for idx,val in enumerate(input[0:5]):
        if (val == 'A'):
            temp += matrix[idx][0]
        elif (val == 'C'):
            temp += matrix[idx][1]
        elif (val == 'G'):
            temp += matrix[idx][2]
        elif (val == 'T'):
            temp += matrix[idx][3]
    if (temp > probability):
        output = input[0:5]
        probability = temp
    input = input[1:]

print(output)