#include<stdio.h>
#include<math.h>
int main()
{
	freopen("fact.in","r",stdin);
	freopen("fact.out","w",stdout);
	long p,n,i,j;
	scanf("%ld",&p);
	i=0;
	j=1;
	if(p==0)
		printf("1");
	else
	{
		while(p>=pow(5,j))
			j++;
		p=p-(j*(j+1))/2+j;
		while(p!=0)
		{
			i=i+5;
			p--;
		}
	printf("%ld",i);
	}
	return 0;
}