#include <stdio.h>
#include <stdlib.h>

int cnt = 0;

int main()
{
        long int  N;
        scanf( "%ld\n", &N );
        int ** masu;

        N = (N + 1)/2;
        printf("%ld\n", ( N * ( N + 1 ) /2 ));

        return 0;
}