#include<stdio.h>

int solutie(int n)
{
 int x=1,sol=0;
 while(x<=n)
 {
  x=x*5;
  sol=sol+n/x;
 }
 return sol;
}
	 
int main()
{
 int a=-1,m,x,y,p,ok=0;
 
 FILE *f=fopen("fact.in","r");
 FILE *g=fopen("fact.out","w");

 fscanf(f,"%d",&p);
 if(p==0)
	 fprintf(g,"1");
 else
    {
	 x=5; y=500000000;
	 while(x<=y)
	 {
	  m=(x+y)/2;
	  if(y==(x+1))
	  {
	   if(solutie(x)==p)
		{
		 ok=1;
		 a=x;
	    }
	   if(solutie(y)==p)
		{
		 ok=1;
		 a=y;
	    }
	   x=y+1;
	  }
	  if(solutie(m)<p&&x<=y)
	     x=m;
	  if(solutie(m)>p&&x<=y)
	     y=m;
	  if(solutie(m)==p&&x<=y)
		{
		 ok=1;
		 a=m;
		 x=y+1;
	    }
	 }
	 if(ok==1)
	  while(a%5!=0)
		 a--;
     fprintf(g,"%d",a);
    }
}