Function to calculate the sum of numbers divisible by 2 or 7
int sum ( int N ) { int S1 , S2 , S3 ; S1 = ( ( N / 2 ) ) * ( 2 * 2 + ( N / 2 - 1 ) * 2 ) / 2 ; S2 = ( ( N / 7 ) ) * ( 2 * 7 + ( N / 7 - 1 ) * 7 ) / 2 ; S3 = ( ( N / 14 ) ) * ( 2 * 14 + ( N / 14 - 1 ) * 14 ) / 2 ; return S1 + S2 - S3 ; }