How much is 1 + 2 + 3 + 4 + 5 added to 100

How much is 1 + 2 + 3 + 4 + 5 added to 100

The formula Sn = n (a1 + an) / 2 or Sn = Na1 + n (n-1) d / 2 D is used as tolerance (here is 1) for summation of arithmetic sequence
(1+100)*(100/2)=5050