A signal $ x(t)=2 \cos (180 \pi t) \cos (60 \pi t)$ is sampled at $ 200 \mathrm{~Hz} $ and then passed through an ideal low pass filter having cut-off frequency of $100 \mathrm{~Hz}.$
The maximum frequency present in the filtered signal in $ \mathrm{Hz}$ is ________ (Round off to the nearest integer).