n,m = map(int,input().split())
two,five = 0,0
k = 2
while k <= n:
two += n//k
k*=2
k = 5
while k <= n:
five += n//k
k*=5
k = 2
while k <= m:
two -= m//k
k*=2
k = 5
while k <= m:
five -= m//k
k*=5
k = 2
while k <= n-m:
two -= (n-m)//k
k*=2
k = 5
while k <= n-m:
five -= (n-m)//k
k*=5
print(min(two,five))