with open('fact.in', 'r') as f:
    nr= int(f.readline())

def fact(n):
    prod = 1
    for i in range(1,n+1):
        prod*=i
    return prod

def finalZ(n):
    total = 0
    while n%10 == 0:
        total+=1
        n = n/10
    return total

def finalnZ(n):
    total = 0
    while n%10 == 0:
        n = n/10
    return n%10

lastnz = 1
totalz = 0
n = 2

while totalz != nr:
    lastdigit = lastnz*n
    totalz += finalZ(lastdigit)
    lastnz = finalnZ(lastdigit)
    n+=1

print(n-1)

##for i in range(0,101,5):
##    fac = fact(i)
##    print(i, " ", finalZ(fac)," ",fac)