c-gcc, 74 bytes

Result

AC

Duration

799ms

Code [DL]

c;main(d,b){c=getchar();putchar(d*b?c:99),b|d&&main(c%7?++d%51:1,~c%2*b);}

stdin

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  K                                               

stdout

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  Kccccccccccccccccccccccccccccccccccccccccc

stderr

/tmp/code.c:1:1: warning: data definition has no type or storage class
 c;main(d,b){c=getchar();putchar(d*b?c:99),b|d&&main(c%7?++d%51:1,~c%2*b);}
 ^
/tmp/code.c:1:1: warning: type defaults to 'int' in declaration of 'c' [-Wimplicit-int]
/tmp/code.c:1:3: warning: return type defaults to 'int' [-Wimplicit-int]
 c;main(d,b){c=getchar();putchar(d*b?c:99),b|d&&main(c%7?++d%51:1,~c%2*b);}
   ^~~~
/tmp/code.c: In function 'main':
/tmp/code.c:1:3: warning: type of 'd' defaults to 'int' [-Wimplicit-int]
/tmp/code.c:1:3: warning: type of 'b' defaults to 'int' [-Wimplicit-int]
/tmp/code.c:1:15: warning: implicit declaration of function 'getchar' [-Wimplicit-function-declaration]
 c;main(d,b){c=getchar();putchar(d*b?c:99),b|d&&main(c%7?++d%51:1,~c%2*b);}
               ^~~~~~~
/tmp/code.c:1:15: note: 'getchar' is defined in header '<stdio.h>'; did you forget to '#include <stdio.h>'?
+#include <stdio.h>
 c;main(d,b){c=getchar();putchar(d*b?c:99),b|d&&main(c%7?++d%51:1,~c%2*b);}
               ^~~~~~~
/tmp/code.c:1:25: warning: implicit declaration of function 'putchar' [-Wimplicit-function-declaration]
 c;main(d,b){c=getchar();putchar(d*b?c:99),b|d&&main(c%7?++d%51:1,~c%2*b);}
                         ^~~~~~~
/tmp/code.c:1:34: warning: '*' in boolean context, suggest '&&' instead [-Wint-in-bool-context]
 c;main(d,b){c=getchar();putchar(d*b?c:99),b|d&&main(c%7?++d%51:1,~c%2*b);}
                                 ~^~

strace