11 S=0
12 PRINT "N,X,Y"
15INPUT N,X0,Y0
16X=X0:Y=Y0
20FOR I=1TO N-1
22 PRINT "X";I;",Y";I
25 INPUT X1,Y1
30     S=S+(X+X1)*(Y-Y1) 
35     X=X1
40     Y=Y1
45 NEXT I
50 PRINT "A=";(S+(X+X0)*(Y+Y0))/2
55 PRINT "MORE INPUT (1=YES,0=NO)"
60 INPUT I
65 IF I=1THEN 11
70 END 

