Input 3 sides of triangle, determine if EQUILATERAL, ISOSCELES, or SCALENE; I tried the if-statement many times but its not working

/*The instruction is ask user to input 3 sides of triangle then determine if EQUILATERAL, ISOSCELES, or SCALENE; I tried the if-statement many times but its not working. */

:TRIANGLE
echo AREA OF TRIANGLE
echo Input First Side:
set /p a=
echo Input Second Side:
set /p b=
echo Input Third Side:
set /p c=
set E=EQUILATERAL
set I=ISOSCELES
set S=SCALENE
Pause
goto Top