function eks = kctr(kk)
k=[];
temp=[];
post=[];
 k = kk;
 l=size(kk);%mencari ukuran kata kunci
 %melakukan ekstrak huruf yang sama
 for i=1:l(1,2)-1
    if double(k(i))~=32
        for j=i+1 : l(1,2)
            if k(i) == k(j)
                k(j)='@';
            end
        end
    else
        k(i) = '@';
    end
 end
 %menampilkan hasil ekstrak
 j=1;
 for i =1 : l(1,2)
     if k(i)~='@'
         temp(j) = k(i);
         j = j+1;
     end
     l = size(k);
 end
 %fprintf('%s\n',eks);

 %buat pemetaan kunci
 for i = 1 : 26
     map(1,i) = char(96+i);
 end
 l = size(temp);
 %fprintf('%d\n',l);
 
 mapsem = map(1,:);
 x=0;
 for i = 1 : 26
     for j = 1 : l(1,2)
         if mapsem(i) == temp(j)
             mapsem(i)='@';
             x= x+1;
         end
     end
 end
 %fprintf('%s\n',mapsem);
 for i = 1 : 26
     if mapsem(i) ~= '@'
         temp(x+1) = mapsem(i);
         x = x+1;
     end
 end
 %fprintf('%s\n',temp);
 %buat ngurutin
 for i= 1 : l(1,2)
    post(i) = temp(i);
 end
 
 for i = 1 : l(1,2)-1
    y = i;
    for j = i+1 : l(1,2)
        if post(y) > post(j)
           y = j;    
        end   
    end
    p       = post(y);
    post(y) = post(i);
    post(i) = p;
 end
 %fprintf('%s\n',post);
 
 z = 1;
 for i = 1:l(1,2)
     for j = 1 : l(1,2)
         if temp(j) == post(i)
             %fprintf('%d\n',z);
             eks(z) = char(temp(j));
             m = j;
             z = z+1;
             while m <= 26
                m = m + l(1,2);
                if m > 26
                    break;
                end
               
                eks(z) = char(temp(m));
                 z = z+1;
             end             
         end
     end
 end
 return