def count7(n, acc=0):
    if n <= 0:
        return acc
    while n > 0:
        v = n
        while v > 0:
            v, r = v // 10, v % 10
            if r == 7:
                acc += 1
        n -= 1
    return acc

if __name__ == "__main__":
    print(count7(6))    # 0
    print(count7(7))    # 1
    print(count7(20))   # 2
    print(count7(70))   # 8
    print(count7(100))  # 20
    print(count7(1000)) # 300