How to PREDICATE data using ANN toolbox?

Dear friends, My question is simple. How to predicate data with ANN? My data is like this:

1, 999919

2, 999824

3, 999730

4, 999635

5, 999540

6, 999445

7, 999350

8, 999255

9, 999160

...

data = xlsread('data.xlsx');
targets = data(:,2);
targets_train = targets(1:900);
targetSeries = tonndata(targets_train,false,false);
feedbackDelays = 1:5;
hiddenLayerSize = 30;
net = narnet(feedbackDelays,hiddenLayerSize);
net.inputs{1}.processFcns = {'removeconstantrows','mapminmax'};
[inputs,inputStates,layerStates,targets] = preparets(net,{},{},targetSeries);
net.divideFcn = 'dividerand';
net.divideMode = 'time';
net.divideParam.trainRatio = 85/100;
net.divideParam.valRatio = 10/100;
net.divideParam.testRatio = 5/100;
net.trainFcn = 'trainlm';
net.performFcn = 'mse';
net.plotFcns = {'plotperform','plottrainstate','plotresponse', 'ploterrcorr', 'plotinerrcorr'};
[net,tr] = train(net,inputs,targets,inputStates,layerStates);
outputs = net(inputs,inputStates,layerStates);
errors = gsubtract(targets,outputs);
performance = perform(net,targets,outputs)
trainTargets = gmultiply(targets,tr.trainMask);
valTargets = gmultiply(targets,tr.valMask);
testTargets = gmultiply(targets,tr.testMask);
trainPerformance = perform(net,trainTargets,outputs)
valPerformance = perform(net,valTargets,outputs)
testPerformance = perform(net,testTargets,outputs)

I want to forecast what is 901st data? How?