2j

def sum_of_descending_series(a, d, n):
    return (n / 2) * (2 * a + (n - 1) * d)

a = 60  # First term
d = -3  # Common difference
n = (a - 1) // abs(d) + 1  # Number of terms
sum = sum_of_descending_series(a, d, n)
print("Sum of the series:", sum)