#include<stdio.h>
#include<math.h>
int ok(int n)
{
     int s=0,nr=5;
     while(n/nr)
     {
          s=s+n/nr;
          nr=nr*5;
     }
     return s;
}
int cautb(int st,int dr,int p)
{
     int med,aux,last=-1;
     while(st<=dr)
     {
          med=st+ (dr-st)/2;
          aux=ok(med);
          if(aux>=p)
          {
               last=med;
               dr=med-1;
          }
          else
          {
               st=med+1;
          }
     }
     return last;
}
int main()
{
     freopen("factorial.in","r",stdin);
     freopen("factorial.out","w",stdout);
     int p;
     scanf("%d",&p);
     printf("%d\n",cautb(1,1000000000,p));
     return 0;
}