progs/a599.py


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def No_of_Triangle(N,K):
    if (N < K):
        return -1;
    else:
        Tri_up = 0;
        Tri_up = ((N - K + 1) *(N - K + 2)) // 2;
        Tri_down = 0;
        Tri_down = ((N - 2 * K + 1) *(N - 2 * K + 2)) // 2;
        return Tri_up + Tri_down;