解法如下：

int a, b;

scanf("%d%d", &a, &b);

if(a - b < 0) { //b > a

    a += a % 2 != 0;

    b -= b % 2 != 0;

    cout << (a + b) * ((b - a) / 2 + 1) / 2 << endl;

} else { //a > b

    a -= a % 2 != 0;

    b += b % 2 != 0;

    cout << (a + b) * ((a - b) / 2 + 1) / 2 << endl;

}