#include <stdio.h>

FILE *f,*g;
long long n,i,temp;
char ok;

long long calcp5(long long x)
{
  long long k,contor;
  k=5;
  contor=0;
  while(x/k!=0)
    {
	  contor+=x/k;
	  k*=5;
	}
  return contor;
}

int main()
{
  f=fopen("fact.in","r");
  g=fopen("fact.out","w");
  fscanf(f,"%lld\n",&n);
  i=5;
  ok=0;
  while(!ok)
    {
	  temp=calcp5(i);
	  if(temp==n) ok=1;
	  i++;
	} 
  fprintf(g,"%lld\n",i-1);
  fclose(f);   fclose(g);
  return 0;
}