def f(n):
    s = ""
    while n > 0:
        s += str(n % 5)
        n //= 5
    s = s[::-1]
    return s

for x in range(1, 1000):
    n = 4 * 625**1920 + 4 * 125**x - 4 * 25**1940 - 3 * 5**1950 - 1960
    if f(n).count('0') == 1891:
        print(x)
        break