#include <fstream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int n,p,ad,s,nn;
int main()
{
   f>>p;
   n=1;
   ad=0;
   while(ad==0)
   {
       s=0;
       nn=n;
       while(nn)
       {
           s=s+nn/5;
           nn=nn/5;
       }
       if(s>=p) ad=1;
    n++;
   }
   n--;
   g<<n;
    return 0;
}