put the frogs on a coordinate plane so that the bottom left frogs coordinates are (0,0), top left frog’s coordinates are (0,1), and top right frog’s coordinates are (1,1). Observe that when a frog jumps, the parity of its coordinates is invariant therefore, none of the frogs can ever get to the bottom right corner, where the coordinates are (1, 0). Another way to say this is that none of the frogs have (odd, even) coordinates, and therefore, they can never land on an (odd, even) point