function A(i: integer; j: integer): integer;
begin
	if (i >= 2) and (j >= 2) then begin
		//writeln("A(",i,",",j,") = A(",i-1,", A(",i,",",j-1,"+1)<br>");
		A := A(i-1, A(i, j-1)+1);
	end
	else
	if (i >=2) and (j = 1) then begin
		//writeln("A(",i,",",j,") = A(",i-1,",2)");
		A := A(i-1, 2);
	end
	else
	if (i = 1) and (j>= 1) then begin
		//writeln("A(",i,",",j,") = ",j);
		A := j;
	end
	else begin
		//writeln("A(",i,",",j,") = -1");
		A := -1;
	end;
end;
var
	i,x,y : integer;
begin
		readln (x,y);
		write(A(x,y));
end.

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