#include <stdio.h>

int main()
{
   FILE *fin=fopen("fact.in", "r");
   FILE *fout=fopen("fact.out", "w");

   int p;
   fscanf(fin, "%ld", &p);

   long n=1, ok=0,s,c;

   while(!ok)
   {
     s=0; c=5;
     while(n/c!=0)
     {
       s+=n/c;
       c*=5; }

     if(s==p) ok=1;
     else n++;
   }

   fprintf(fout, "%ld", n);

   fclose(fin); fclose(fout);

   return 0;
}