unit Unit1;

interface
uses Math;
  type
  TFunc = function(Arg : real): real;
  procedure rightrec(strt, stp, h: real; undint: TFunc);
  function T(Arg: real): real;
  var F: TextFile;
implementation
  var integral, strt, stp, h: real;
      dirOut: string;
      undint: TFunc;
  function T;
  begin
    result := 1/(Arg + 1);
  end;
  procedure rightrec;
  var t: real;
      n, i: integer;
  begin
    n := Round((stp - strt)/h);
    integral := 0;
    for i := 0 to (n-1) do begin
      t := strt + (i + 1)*h;
      integral := integral + h*undint(t);
    end;
  end;
begin
  readln(strt, stp, h);
  dirOut := 'C:\Users\Lenovo\Desktop\out.txt';
  AssignFile(F, dirOut);
  rewrite(F);
  rightrec(strt, stp, h, T);
  writeln(F, integral:4:4);
  CloseFile(F);
end.