# 2019 IUSB Programming Competition
# Round 1 Problem 3
# Count the number of training 0s in n!
# Solution by Dana Vrajitoru
# Uses Python 3.6.2

# Find out how many times we can divide n by 5 exactly
def count5Factors(n):
    count = 0
    while n % 5 == 0:
        count = count + 1
        n = n / 5
    return count

# Count the trailing 0s in n!
# Find out how many times we can divide k by 5 exactly
# for every k between 2 and n
def trailingZeros(n):
    count = 0
    for k in range(2, n+1):
        count += count5Factors(k)
    return count
    
# Testing the function
if __name__ == '__main__':
    print("Enter a number:")
    n = int(input())
    print(trailingZeros(n))