#include <iostream>
#include<cstdio>
#include<cmath>
using namespace std;
int main()
{
    freopen("fact.in","r",stdin);
   freopen("fact.out","w",stdout);
   int p,st,dr,mi,cur,fac,val,la;
   scanf("%d",&p);
   st=1;
   dr=(p+1)*5;
   while(st<=dr)
   {
       mi=(st+dr)/2;
       val=mi;
       cur=0;
       fac=5;
       while(fac<=val)
       {
           cur=cur+val/fac;
           fac=fac*5;
       }
       if(cur<p)
       {
           st=mi+1;
       }
       else
       {
           la=mi;
           dr=mi-1;
       }

   }
   printf("%d\n",la);
    return 0;
}