#include <stdio.h>
int p2,p5,P,i,x,y,cont2,cont5,nr=1;
FILE *in=fopen("fact.in","rt"),*out=fopen("fact.out","wt");

int main()
{
fscanf(in,"%d",&P);
//while(p2!=P||p5!=P)
// {
 for(i=2;i<=200000;i++)
 {
 if(p2<=P||p5!=P)
 {
	cont2=0;
  cont5=0;
  x=i;
	y=i;
	if(x%2==0||y%5==0)
	while(x%2==0||y%5==0)
   {
   if(x%2==0)
    {
    cont2++;
    x/=2;
    }
   if(y%5==0)
    {
    cont5++;
    y/=5;
    }
	 }
	 //if(cont2>cont5)
    p5+=cont5;
   //else
		p2+=cont2;
    nr++;
	}
 }
fprintf(out,"%d",nr);
/*if(p2>p5)
 fprintf(out,"%d",p5);
else
 fprintf(out,"%d",p2);*/
return 0;
}