Using Binary Search:

def solve(n): def count(x): res = 0 while x: t = x//5 res+=t x = t return res

l,r = 5,5*(10**16)
res = 5
while l<=r:
    mid = (l+r)//2
    if count(mid)>=n:
        res = mid
        r = mid - 1
    else:
        l = mid + 1
return res