#include <stdio.h>
FILE *f=fopen("factorial.in","r");
FILE *g=fopen("factorial.out","w");
long n,nr;
int main()
{
	fscanf(f,"%lld",&n);
	if (n!=0)
	{
		nr=n/2*10;
		if(n%2==1)
			nr=nr+5;
		fprintf(g,"%lld",nr);
	}
	else
		fprintf(g,"1");
	fclose(f);
	return 0;
}