function [V1, V2] = mesh_boundaries(V, F)
    VV = zeros(size(V, 1));
    for i = 1 : size(F, 1)
        a = F(i, 1);
        b = F(i, 2);
        c = F(i, 3);
        if a > b
            VV(b, a) = VV(b, a) + 1;
        else
            VV(a, b) = VV(a, b) + 1;
        end
        if a > c
            VV(c, a) = VV(c, a) + 1;
        else
            VV(a, c) = VV(a, c) + 1;
        end
        if c > b
            VV(b, c) = VV(b, c) + 1;
        else
            VV(c, b) = VV(c, b) + 1;
        end
    end

    trisurf(F, V(:, 1), V(:, 2), V(:, 3));
    for i = 1 : size(VV, 1)
        for j = 1 : size(VV, 2)
            if VV(i, j) == 1
                hold on;
                plot3([V(i, 1); V(j, 1)], [V(i, 2); V(j, 2)], [V(i, 3); V(j, 3)], 'r');
            end
        end
    end
    hold off;
end