There is no jump keyword in Matlab. You can just check like
N=input('enter the number :');
N1=find(XY(:,1)==N); %find the value from XY first column
if isempty(N1)
errordlg('Value does not exist!')
else
N2=XY(N1,[2,3]); %this will show corresponding value of N1
X6=N2(1);
Y6=N2(2);
end
Or, if you want to insist on a correct value:
N1=[];
while isempty(N1)
N=input('enter the number :');
N1=find(XY(:,1)==N); %find the value from XY first column
end
N2=XY(N1,[2,3]) %this will show corresponding value of N1
X6=N2(1);
Y6=N2(2);