import sys

n=int(sys.stdin.readline())
val=1
for i in range(1,n+1):
    val=val*i

s=list(str(val))

length=len(s)
# print(s)
count=0
for i in range(length-1,0,-1):
    # print(s[i])
    if int(s[i])==0:
        count=count+1
    else:
        break
print(count)