#!/usr/bin/env python
# 2022 - Advent Of Code 6

# file = 'input_example.txt'
file = 'input.txt'

previous = []
count = 0
with open(file, encoding="utf-8") as f:
    signal = f.readline().strip()
    for c in signal:
        count += 1
        if c in previous:
            pos = previous.index(c)
            # print(f'[{count}]{c} already found at {pos}')
            previous = previous[pos+1:]
        elif len(previous) == 3:
            print(f'start of signal found at position {count}')
            break
        previous.append(c)