//factorial

#include <stdio.h>
#include <stdlib.h>


int fact(int *p)
{
   int i=2,k2=0,k5=0,j,y;
   	while((k2+k5)/2!=*p)
   	  {
   	  	  y=i;
   	  	  for(j=2;j<=y;j++)
   	  	     {
   	  	     	if(y%j==0)
   	  	     	   {
   	  	     	   	 if(j==2 && k2!=*p) k2++;
   	  	     	   	 if(j==5 && k5!=*p) k5++;
   	  	     	   	 y/=j;
   	  	     	   	 j=1;
   	  	     	   }
   	  	     }
   	  	  i++;
   	  }
   	if(k2==*p && k5==*p) return i-1;
}

int main()
{
	int p;
	FILE *fp,*f;
	fp=fopen("fact.in","r");
	f=fopen("fact.out","w");
	fscanf(fp,"%d",&p);	
	fprintf(f,"%d",fact(&p));
	fclose(fp);
	fclose(f);
}