var
 n,a,b:integer;
 p:array[0..20,0..15,0..15]of extended;
procedure init;
var
 i,j:integer;
begin
 read(n);
 read(a);
 read(b);

 fillchar(p,sizeof(p),0);
 for i:=0 to a do
  for j:=0 to b do
   p[0,i,j]:=1;
 for i:=0 to n do p[i,0,0]:=1;

end;
procedure solve(n,a,b:integer);
var
 i,j:integer;
begin
 if n>=1 then
  for i:=0 to a do
   for j:=0 to b do
    begin
     if p[n-1,i,j]=0 then
      solve(n-1,i,j);
     p[n,a,b]:=p[n,a,b]+p[n-1,i,j];
    end;
end;
begin
 init;
 solve(n,a,b);
 writeln(p[n,a,b]:0:0);
end.