Pass the Squares (1190)

Draw a path that passes orthogonally through centers of cells. The path must start at the cell marked 'S' and finish at the cell marked 'F'. Some 4-cell square regions are shaded. The path must enter exactly one cell in every shaded square region (and not enter the 3 other cells). The path cannot cross itself or enter any cell more than once.

Reference: WPF (1)