Find the sum of 1, negative 2,. 3, negative 4,5, negative 6,7, negative 8.99, negative 100 integers, and calculate the formula

Find the sum of 1, negative 2,. 3, negative 4,5, negative 6,7, negative 8.99, negative 100 integers, and calculate the formula

1-2+3-4+5-6+.+99-100
=(1-2)+(3-4)+...+(99-100)
=-1x50
=-50