c-gcc, 65 bytes

Result

AC

Duration

742ms

Code [DL]

a,c[99];main(i){putchar(a=c[i]|=getchar()|a&1)%13&&main(i%51+1);}

stdin

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     K                                            

stdout

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     k!!!!!!!!!!!!!u

stderr

/tmp/code.c:1:1: warning: data definition has no type or storage class
 a,c[99];main(i){putchar(a=c[i]|=getchar()|a&1)%13&&main(i%51+1);}
 ^
/tmp/code.c:1:1: warning: type defaults to 'int' in declaration of 'a' [-Wimplicit-int]
/tmp/code.c:1:3: warning: type defaults to 'int' in declaration of 'c' [-Wimplicit-int]
 a,c[99];main(i){putchar(a=c[i]|=getchar()|a&1)%13&&main(i%51+1);}
   ^
/tmp/code.c:1:9: warning: return type defaults to 'int' [-Wimplicit-int]
 a,c[99];main(i){putchar(a=c[i]|=getchar()|a&1)%13&&main(i%51+1);}
         ^~~~
/tmp/code.c: In function 'main':
/tmp/code.c:1:9: warning: type of 'i' defaults to 'int' [-Wimplicit-int]
/tmp/code.c:1:17: warning: implicit declaration of function 'putchar' [-Wimplicit-function-declaration]
 a,c[99];main(i){putchar(a=c[i]|=getchar()|a&1)%13&&main(i%51+1);}
                 ^~~~~~~
/tmp/code.c:1:33: warning: implicit declaration of function 'getchar' [-Wimplicit-function-declaration]
 a,c[99];main(i){putchar(a=c[i]|=getchar()|a&1)%13&&main(i%51+1);}
                                 ^~~~~~~
/tmp/code.c:1:33: note: 'getchar' is defined in header '<stdio.h>'; did you forget to '#include <stdio.h>'?
+#include <stdio.h>
 a,c[99];main(i){putchar(a=c[i]|=getchar()|a&1)%13&&main(i%51+1);}
                                 ^~~~~~~
/tmp/code.c:1:44: warning: suggest parentheses around arithmetic in operand of '|' [-Wparentheses]
 a,c[99];main(i){putchar(a=c[i]|=getchar()|a&1)%13&&main(i%51+1);}
                                           ~^~
/tmp/code.c:1:50: warning: value computed is not used [-Wunused-value]
 a,c[99];main(i){putchar(a=c[i]|=getchar()|a&1)%13&&main(i%51+1);}
                                                  ^~

strace