main

echo "Enter 1st side."
read a
echo "Enter 2nd side."
read b
echo "Enter 3rd side."
read c
echo "Enter 4th side."
read d

if [[ $a == $b && $b == $c && $c == $d ]]
then
    echo "Valid."
elif [[ $a == $b && $c == $d ]]
then
    echo "Valid."
elif [[ $a == $d && $c == $b ]]
then
    echo "Valid."
elif [[ $a == $c && $d == $b ]]
then 
    echo "Valid."
else
    echo "Not Valid."
fi