[Borek]

I = ? m_ir_i² = m₁r₁² + m₂r₂²

so we need r₁ and r₂. They can be found as coordinates of mass center, that are described by conditions:

r₁ + r₂ = R
m₁r₁ = m₂r₂

that gives

r₁ = Rm₂/(m₁+m₂)
r₂ = Rm₁/(m₁+m₂)

these must be entered into I formula given above, and when rearranged it gives

I = ?R²

quite interesting exercise if you have not done such things in the last 20 years

Mitch, did I told you LaTeX will be handy?