#include<stdio.h>

int i,p,count,n,c,ok;

int main()
{

 freopen("fact.in","r",stdin);
 freopen("fact.out","w",stdout);

 scanf("%d",&p);

 n--;
 for(i=5;count<=p;i=i+5)

 {

  n++;

  c = i;

  ok = 0;

  while(c)

  {
    if(c%5==0)

     ok++;

    c /= 5;

  }

  if(ok>0)

   count += ok;

   else

   count++;

  }

 if(p==0)

 printf("1");
 else
 printf("%d",n*5);

 return 0;
}