node, 148 bytes

Result

AC

Duration

782ms

Code [DL]

a=require("fs").readFileSync(0);for(i=51;i<a.length;i+=51)for(j=0;j<50;j++)a[i+j]+=a[j]-32;i-=51;while(a[++i]!=84)a[i]+=a[i-1]-32;console.log(""+a);

stdin

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                     K                            

stdout

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                     KKKKT                        

stderr

strace