data stock2;
    set stock;
    Time = _n_;
run;

data future;
    input y Time;
    datalines;
    . 121
    . 122
    . 123
    . 124
    . 125
    . 126
    . 127
    . 128
    . 129
    . 130
run;

data stock3;
    update stock2 future;
    by Time;
run;

proc arima data=stock3;
identify var=stock(1,12) crosscorr=(Time);
estimate input = (Time) printall;
forecast lead = 10;
run;