n = int(eval(input()))

ans = 0

a = 1

na = n

if n % 2 == 1:

    print((0))

else:

    # for i in range(3):

    #     n100 = n // 100

    #     n50 = n // 50

    #     n = n // 10

        

    #     ans += n + n50 - n100

    #     print(n,n50,n100)

    # print(ans)





        # for i in range(1,20):

        #     for j in range(1,40):

        #         ans += (n // ((5**j)*(10**i)))

        #     # ans += (n //(5*10**i))

        # n10 = n // 10

        # print(ans+n10)



    for j in range(1,40):

        ans += (n // ((5**j)*10))

    n10 = n // 10

    print((ans+n10))



# while na != 0:

#     a *= na

#     na -= 2

# # print(a)

# a = list(str(a))

# i = -1

# cnt = 0

# # print(a)

# while a[i] == "0":

#     cnt += 1

#     i -= 1

# print(cnt)
n = int(eval(input()))

ans = 0

if n % 2 == 1:

    print((0))

    exit()



for i in range(50):

    if n >= 10*(5**(i)):

        ans += n//(10*(5**(i)))

print(ans)

n = int(eval(input()))
ans = 0
a = 1
na = n
if n % 2 == 1:
    print((0))
else:
    # for i in range(3):
    #     n100 = n // 100
    #     n50 = n // 50
    #     n = n // 10
    #     ans += n + n50 - n100
    #     print(n,n50,n100)
    # print(ans)
    # for i in range(1,20):
    #     for j in range(1,40):
    #         ans += (n // ((5**j)*(10**i)))
    #     # ans += (n //(5*10**i))
    # n10 = n // 10
    # print(ans+n10)
    for j in range(1, 40):
        ans += n // ((5**j) * 10)
    n10 = n // 10
    print((ans + n10))
# while na != 0:
#     a *= na
#     na -= 2
# # print(a)
# a = list(str(a))
# i = -1
# cnt = 0
# # print(a)
# while a[i] == "0":
#     cnt += 1
#     i -= 1
# print(cnt)

n = int(eval(input()))
ans = 0
if n % 2 == 1:
    print((0))
    exit()
for i in range(50):
    if n >= 10 * (5 ** (i)):
        ans += n // (10 * (5 ** (i)))
print(ans)

-a = 1 -na = n -else: -    # for i in range(3): -    #     n100 = n // 100 -    #     n50 = n // 50 -    #     n = n // 10 -    #     ans += n + n50 - n100 -    #     print(n,n50,n100) -    # print(ans) -    # for i in range(1,20): -    #     for j in range(1,40): -    #         ans += (n // ((5**j)*(10**i))) -    #     # ans += (n //(5*10**i)) -    # n10 = n // 10 -    # print(ans+n10) -    for j in range(1, 40): -        ans += n // ((5**j) * 10) -    n10 = n // 10 -    print((ans + n10)) -# while na != 0: -#     a *= na -#     na -= 2 -# # print(a) -# a = list(str(a)) -# i = -1 -# cnt = 0 -# # print(a) -# while a[i] == "0": -#     cnt += 1 -#     i -= 1 -# print(cnt) +    exit() +for i in range(50): +    if n >= 10 * (5 ** (i)): +        ans += n // (10 * (5 ** (i))) +print(ans)