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

int main()
{
fscanf(in,"%d",&P)
while(p2!=P&&p5!=P)
 {
 for(i=1;i<=1000;i++)
 {
  x=i;
  y=i;
  while(x%2!=0&&y%2!=0)
   {
   if(x%2==0)
    {
    cont2++;
    x/=2;
    }
   if(y%5==0)
    {
    cont5++;
    x/=5;
    }
   }
   if(cont2>cont5)
    p5+=cont5;
   else
    p2+=cont2;
  }
 }
if(p2>p5)
 fprintf(out,"%d",p5);
else
 fprintf(out,"%d",p2);
return 0;
}