#include<stdio.h>
int main()
{
	long a,b;
	freopen ("fact.in","r",stdin);
	freopen ("fact.out","w",stdout);
	scanf("%i",&a);
	b=a*5;
    a--;
	while (a%10!=0&&a%10!=5)
		a--;
	b-=a;
	printf("%i",b);
	return 0;
}