decryption text using hill cipher

hi what is the wrong in program , why inverse of key equal zero

clc;

clear all;

close all;

k=[17 17 5; 21 18 21;2 2 19];

c=input('enter theciphertext','s');

c=upper(c);

x=length(c);

d=mod(det(k),26);

a=[1 3 5 7 9 11 15 17 19 21 23 25];

b=[1 9 21 15 3 19 7 23 11 5 17 25];

s=0;

for i=1:12

if a(i)==d;

s=i;

end

end

id=b(s);

adj=round(inv(k)*d);

adj=mod(adj,26);

ik=mod(adj*id,26);

for i=1:3:x

r=double(c(i:i+2))'-65;

p(i:i+2)=mod(ik*r,26);

end

p=char(p+97);

[Walter Roberson]

what is a sample input and expected output?