ruby, 75 bytes

Result

WA

Duration

556ms

Code [DL]

print gets.chars.each_with_index.map{ |i,c| ((i.ord+c-64)%26+65).chr }.join

stdin

KCHJTCXDXOVNXAYHPJHZYIPIZD

stdout

LEKNYIELGYGZKONXGBATTEMGYDY

stderr

strace