c-gcc, 78 bytes

Result

AC

Duration

791ms

Code [DL]

b,c;main(d){for(;~(c=getchar());d=84>c?++d%51:1)putchar(!d|b?99:c),b=c&1|b*d;}

stdin

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                    K                             

stdout

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                    Kccccc                        

stderr

/tmp/code.c:1:1: warning: data definition has no type or storage class
 b,c;main(d){for(;~(c=getchar());d=84>c?++d%51:1)putchar(!d|b?99:c),b=c&1|b*d;}
 ^
/tmp/code.c:1:1: warning: type defaults to 'int' in declaration of 'b' [-Wimplicit-int]
/tmp/code.c:1:3: warning: type defaults to 'int' in declaration of 'c' [-Wimplicit-int]
 b,c;main(d){for(;~(c=getchar());d=84>c?++d%51:1)putchar(!d|b?99:c),b=c&1|b*d;}
   ^
/tmp/code.c:1:5: warning: return type defaults to 'int' [-Wimplicit-int]
 b,c;main(d){for(;~(c=getchar());d=84>c?++d%51:1)putchar(!d|b?99:c),b=c&1|b*d;}
     ^~~~
/tmp/code.c: In function 'main':
/tmp/code.c:1:5: warning: type of 'd' defaults to 'int' [-Wimplicit-int]
/tmp/code.c:1:22: warning: implicit declaration of function 'getchar' [-Wimplicit-function-declaration]
 b,c;main(d){for(;~(c=getchar());d=84>c?++d%51:1)putchar(!d|b?99:c),b=c&1|b*d;}
                      ^~~~~~~
/tmp/code.c:1:22: note: 'getchar' is defined in header '<stdio.h>'; did you forget to '#include <stdio.h>'?
+#include <stdio.h>
 b,c;main(d){for(;~(c=getchar());d=84>c?++d%51:1)putchar(!d|b?99:c),b=c&1|b*d;}
                      ^~~~~~~
/tmp/code.c:1:34: warning: operation on 'd' may be undefined [-Wsequence-point]
 b,c;main(d){for(;~(c=getchar());d=84>c?++d%51:1)putchar(!d|b?99:c),b=c&1|b*d;}
                                 ~^~~~~~~~~~~~~~
/tmp/code.c:1:49: warning: implicit declaration of function 'putchar' [-Wimplicit-function-declaration]
 b,c;main(d){for(;~(c=getchar());d=84>c?++d%51:1)putchar(!d|b?99:c),b=c&1|b*d;}
                                                 ^~~~~~~
/tmp/code.c:1:57: warning: suggest parentheses around operand of '!' or change '|' to '||' or '!' to '~' [-Wparentheses]
 b,c;main(d){for(;~(c=getchar());d=84>c?++d%51:1)putchar(!d|b?99:c),b=c&1|b*d;}
                                                         ^~
/tmp/code.c:1:71: warning: suggest parentheses around arithmetic in operand of '|' [-Wparentheses]
 b,c;main(d){for(;~(c=getchar());d=84>c?++d%51:1)putchar(!d|b?99:c),b=c&1|b*d;}
                                                                      ~^~

strace