In thermogravimetric analysis, 12.45 mg of CuSO4.5H2O was subjected to heating under N2 atmosphere. At a particular temperature, there was a weight loss of 3.6 mg. The number of water molecule(s) lost per formula unit is _____. (Given molar mass (in g mol-1) of H = 1.0, O = 16.0, S = 32.0, and Cu = 63.5) (rounded off to the nearest integer)