OPEN "inut.txt" FOR INPUT AS #1
INPUT #1, x1, y1
INPUT #1, x2, y2
INPUT #1, x3, y3
CLOSE #1
l1 = SQR((x1 - x2) ^ 2 + (y1 - y2) ^ 2)
l2 = SQR((x2 - x3) ^ 2 + (y2 - y3) ^ 2)
l3 = SQR((x3 - x1) ^ 2 + (y3 - y1) ^ 2)
p = l1 + l2 + l3
OPEN "output.txt" FOR OUTPUT AS #1
PRINT #1, p