c-gcc, 54 bytes

Result

AC

Duration

555ms

Code [DL]

main(i){for(;i<27;)putchar((getchar()-13+i++)%26+65);}

stdin

HKHIESQMCNSXAPDDFOICPITVYL

stdout

IMKMJYXULXDJNDSTWGBWKEQTXL

stderr

/tmp/code.c:1:1: warning: return type defaults to 'int' [-Wimplicit-int]
 main(i){for(;i<27;)putchar((getchar()-13+i++)%26+65);}
 ^~~~
/tmp/code.c: In function 'main':
/tmp/code.c:1:1: warning: type of 'i' defaults to 'int' [-Wimplicit-int]
/tmp/code.c:1:20: warning: implicit declaration of function 'putchar' [-Wimplicit-function-declaration]
 main(i){for(;i<27;)putchar((getchar()-13+i++)%26+65);}
                    ^~~~~~~
/tmp/code.c:1:29: warning: implicit declaration of function 'getchar' [-Wimplicit-function-declaration]
 main(i){for(;i<27;)putchar((getchar()-13+i++)%26+65);}
                             ^~~~~~~

strace