Function to return the nth term of the required sequence
int nth_term ( int a , int b , int n ) { int z = 0 ; if ( n % 6 == 1 ) z = a ; else if ( n % 6 == 2 ) z = b ; else if ( n % 6 == 3 ) z = b - a ; else if ( n % 6 == 4 ) z = - a ; else if ( n % 6 == 5 ) z = - b ; if ( n % 6 == 0 ) z = - ( b - a ) ; return z ; }