Using Locator coordinates for function in a 3D-Model
===

I have a  plot with a locator on it. I would like to get the locator's y coordinate for "n" in my 3D-model(n=IntegerPart of y). (Click on a plot should change the number of molecules in the cube) I'm a new user and have some difficulties with understanding the syntax. I would be very grateful for any help in connecting two parts (plot and 3D) together.         
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Thank you! 
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    a = Graphics[{White, Table[Circle[{0, 0}, i], {i, 3}]}, 
    ImageSize -> 1];

    Manipulate[
     Show[Plot[Po*E^(-c*t/V), {t, 0, 10}, 
      PlotLabel -> Column[{"Pressure= " <> ToString[Po*E^(-c*p[[1]]/V)] <> 
       ToString[Pa], "Time=" <> ToString[p[[1]]] <> ToString[s]}],  
      AxesLabel -> {"t", "P(t)"}, PlotStyle -> Thickness[0.01], 
      PlotRange -> All], 
        Graphics[Locator[{p[[1]], Po*E^(-c*p[[1]]/V)}]]], {V, 1, 30}, {c, 
     0, 30}, {Po, 100, 300}, {{p, {1, 1}}, Locator, Appearance -> a}]



      WallReflexion[atom_] := 
     Transpose[(Which[#[[1]] < 0 + r, {0 + r, -#[[2]]}, #[[1]] > 
        1 - r, {1 - r, -#[[2]]}, True, #]) & /@ Transpose[atom]];

    propagate[T_, atom_] := {atom[[1]] + 0.01 Sqrt[T/600] atom[[2]], atom[[2]]};

      Manipulate[Module[{},
     If[Length[atoms] < n, 
    atoms = Transpose[{RandomReal[1, {n, 3}], 
      RandomReal[NormalDistribution[0, 1], {n, 3}]}]];

     Pane[Graphics3D[{PointSize[r], Blue, Opacity[.4],Point[Dynamic[atoms = wallReflexion /@ atoms;
       atoms = propagate[30, #] & /@ atoms; First /@ atoms]]}, BoxStyle -> Directive[Dashed], 
        PlotRange -> {{0, 1}, {0, 1}, {0, 1}}, ImageSize -> 300], {300, 
    350}, Alignment -> Center]],{atoms, {{}}, ControlType -> None}]
  
