`S3 = 1 + ( - 3 ) + 5 + ( - 7 ) + ..... + 2001 + ( - 2002 )`
`S3 = [ ( 1 + ( - 3 ) ] + [ ( 5 + ( - 7 ) ] + ..... + [ 2001 + ( - 2002 ) ]`
`S3 = ( - 2 ) + ( - 2 ) + ..... + ( - 2 )`
`S3 = ( - 2 ) . 1001`
`S3 = - 2002`
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`S4 = ( - 1001 ) + ( - 1000 ) + ( - 999 ) + ..... + 1001 + 1002`
`S4 = [ ( - 1001 ) + 1001 ] + [ ( - 1000 ) + 1000 ] + ...... + [ ( - 1 ) + 1 ] + 0 + 1002`
`S4 = 0 + 0 + .... + 0 + 0 + 1002`
`S4 = 0 + 1002`
`S4 = 1002`