Solution used to produce first submission

The solution was has a validation set but doesn't use it.
Logistic regression seem to have high enough bias not to overfit
too badly. The error on the training set (32k samples) ends up
being around 6.5% and the error on the validation set (10k samples)
aound 7.2%. It ran for 2.5k epochs.

result on submission: 0.92071