2i

def sum_of_mixed_series(n):
    # This series alternates between adding 1 and adding 2
    sum = 0
    for i in range(1, n + 1):
        if i % 2 == 0:
            sum += i - 1
        else:
            sum += i
    return sum

n = int(input("Enter the value of N: "))
sum = sum_of_mixed_series(n)
print("Sum of the series:", sum)