number = eval(input())
letter = True
for n in range(len(number)):
    if number[n] == 7 and letter == True:
        print(n)
        letter = False
if letter:
    print("Not found")

a4bf12f7522cd7cc6f730adef1becc99971dd2fc
<mask token>

<mask token>
for n in range(len(number)):
    if number[n] == 7 and letter == True:
        print(n)
        letter = False
if letter:
    print('Not found')

number = eval(input())
letter = True
for n in range(len(number)):
    if number[n] == 7 and letter == True:
        print(n)
        letter = False
if letter:
    print('Not found')

number = eval(input())
letter = True
for n in range(len(number)):
    if number[n] == 7 and letter == True:
        print(n)
        letter = False
if letter:
    print("Not found")
