Cannot get the correct data with if-else in csh script

1. I'm trying to write a script to check whether my input is correct. If I use a script as below, I cannot get the correct data.

#! /bin/csh 
set input_tmp = $1
set input = `echo "$input_tmp" | tr '[a-z]' '[A-Z]'`
echo "Your input must be AAA | BBB"
if ("$input" != "AAA" || "$input" != "BBB") then
        echo "$input : FAIL"
else
        echo "$input : PASS"
endif

When I source and add the input, the result is:

%source check AAA
Your input must be AAA | BBB
AAA : FAIL

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2. If I try to replace "!=" to "==". The script is ok.

#! /bin/csh 
set input_tmp = $1
set input = `echo "$input_tmp" | tr '[a-z]' '[A-Z]'`
echo "Your input must be AAA | BBB"
if ("$input" == "AAA" || "$input" == "BBB") then
        echo "$input : PASS"
else
        echo "$input : FAIL"
endif

---

When I try to test. It's ok.

% source check2 AAA
Your input must be AAA | BBB
AAA : PASS
% source check2 CCC
Your input must be AAA | BBB
CCC : FAIL
---

I don't know why Case 1 does not work because I maybe need to use Case 1 in some cases Please help to review.