Find the sum of all the numbers except the multiples of 3 in the 100 numbers from 1 to 100

Find the sum of all the numbers except the multiples of 3 in the 100 numbers from 1 to 100

1+2+3+..+100-(3+6+9+...+99)
=100*101/2-3(1+2+..+33)
=5050-1683
=3367