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s = '7' * 97 + '8'
while '777' in s or '78' in s:
    if 8 == int(s[-1]):
        if '78' in s:
            s = s.replace('78','7',1)
    elif '777' in s:
        s = s.replace('777','78',1)
    else:
        break
print(s.count("7"))