N = int(input())
a = 1
b = 10 ** 5 + 1

cnt = 0
while cnt < 20:
    i = (a + b) // 2
    d = 10 ** i
    if (d - 1) ** 2 >= N:
        b = i
    else:
        a = i
    cnt += 1        

i = min(1, i - 10)

while True:
    d = 10 ** i
    if (d - 1) ** 2 >= N:
        print(len(str(d)) - 1)
        break
    i += 1