type fff=record
           h:longint;
           x:extended;
         end;
var
 top,kk:extended;
 n:longint;
 a,b,c:fff;

procedure zl;
 var i,j:integer;
     oo:fff;
  begin
   readln(a.h,a.x,c.h,c.x,n);
   if a.h>c.h then begin
                    oo:=a;
                    a:=c;
                    c:=oo;
                   end;
   b.h:=a.h+1;
   if a.h<>c.h-1 then b.x:=(c.x-(c.h-a.h-2)*a.x)/(c.h-a.h-1)
                 else b:=c;
  end;

procedure gc;
 var i:longint;
     a1,b1,c1:extended;
  begin
   if n>b.h then begin i:=b.h;a1:=a.x;b1:=b.x; end
            else begin i:=a.h;a1:=b.x;b1:=a.x; end;
   if n=b.h then begin
                  writeln(trunc(b.x));
                  halt;
                 end;
   if n=a.h then begin
                  writeln(trunc(a.x));
                  halt;
                 end;
   while i<>n do
     if i<n then begin
                  c1:=a1+b1;
                  a1:=b1;
                  b1:=c1;
                  inc(i);
                 end
            else begin
                  c1:=b1-a1;
                  b1:=a1;
                  a1:=c1;
                  dec(i);
                 end;

   writeln(trunc(c1));
  end;

begin
 zl;
 gc;
end.