#include<stdio.h>
main()
{
	char fin[100], fout[100];
	for(int t = 1 ; t <= 5 ; t++ )
	{
		sprintf(fin,".%d.in",t);
		sprintf(fout,".%d.out",t);
		freopen(fin,"r",stdin);
		freopen(fout,"w",stdout);
		int n,i,sum=0;
		scanf("%d",&n);
		for(i=0;i<=n;i++) sum+=(i&1?0:i);
		printf("%d", sum);
	}
}