what is wrong with the following code

i'm trying to do the jacobi method for some linear equations and i'm receiving NaN as a result

%% Input data

n=input('number of ecuations, n:');

ni=input('number of iterations , ni:');

tol=input('tolerance,tol: ');

A=zeros(n,n+1);

x1=zeros(n);

x2=zeros(n);

x1=[1 1 1];

%% Ecuations

%% Ec1: x1 + 5x2 - 6x3 = 5

%% Ec2: 3x1 + x2 + 5x3 = 23

%% Ec3: x1 + 4x2 + x3 = 7

%% System Matrix

a=[1 5 -6 5;3 1 5 23 ;1 4 1 7];

%% Calculus

k=1;

while k<=ni

error=0;

for i=1:n

s=0

for j=i:n

s=s-A(i,j)*x1(j);

end

s=(s+A(1,n+1))/A(i,i);

if abs(s)>error

error=abs(s)

end

x2(i)=x1(i)+s;

end

if error<=tol

break

else

k=k+1;

for i=1:n

x1(i)=x2(i);

end

end

end

fprintf(' solution after %d iterations is :\n' ,k-1);

for i=1:n

fprintf('%11.8f\n',x2(i));

end