A seesaw has a length L and uniform mass m and is resting at an angle of 𝚹 with respect to the ground

 A seesaw has a length L and uniform mass m and is resting at an angle of 𝚹  with respect to the ground (see the following figure). 

The pivot is located at a distance R from the lowered end. 

What magnitude of force needs to be applied perpendicular to the seesaw at the raised end so as to allow the seesaw to barely start to rotate?

Hint: 

F (L-R) = mg (R- L/2) cos 𝚹