#include <bits/stdc++.h>

using namespace std;
ifstream in("fact.in");
ofstream out("fact.out");
long long nr0(long long n)
{
    long long s=0;
  long long p=5;
    while(n>=p)
    {
        s=s+n/p;
        p*=5;
    }
    return s;
}
int main()
{
   int n;
   in>>n;
   long long st=1;
   long long dr=2<<62;
   long long rez=-1;
   while(st<=dr)
   {
      long long mid=(st+dr)/2;
       if(nr0(mid)==n)
       {
           dr=mid-1;
           rez=mid;
       }
       else if(nr0(mid)>n)
       {
           dr=mid-1;
       }
       else{
        st=mid+1;
       }
   }
   out<<rez;
    return 0;
}