main function
static void Main ( ) { Stack < int > s1 = new Stack < int > ( ) ; Stack < int > s2 = new Stack < int > ( ) ; s1 . Push ( 34 ) ; s1 . Push ( 3 ) ; s1 . Push ( 31 ) ; s2 . Push ( 1 ) ; s2 . Push ( 12 ) ; s2 . Push ( 23 ) ;