Select both shapes right-click and convert them to Editable Splines. Pick one of the splines, click Attach (under Geometry rollout) then click on the other one. Right-click to exit from Attach mode. In the Top Viewport, select the vertices as shown (a "4 selected, 1 unselected" pattern). Double check you've selected the right vertices then hit Delete to remove them.
Select the topmost vertex on each of the attached splines. Click on Fuse, then click on Weld. Still in the Vertex mode, hit Ctrl+A to select all vertices, right-click and set the vertex type to Corner.
Select two vertices as shown in the picture below and delete them. Then select the sharp angle vertices and chamfer them until the top of our spline object gets a regular "S" shape.
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