{
ZADATAK: meteor
JEZIK: PASCAL
}
var x,y,r:real;
    i,n,p,q,a,b,pom:longint;
function floor(w:real):longint;
begin
 if w=trunc(w) then floor:=trunc(w) else if w>0 then floor:=trunc(w)
                                         else floor:=trunc(w)-1;
end;
function ceil(w:real):longint;
begin
 if trunc(w)=w then ceil:=trunc(w)
               else ceil:=floor(w)+1;
end;
procedure prvi_kvadrant;
begin
 p:=floor(x);
 q:=floor(y);
 a:=ceil(x+r);
 b:=ceil(y+r);
 n:=n+(a-p)*(b-q);
 i:=b-1;
 pom:=1;
 while (i>q)and(pom>0) do
    begin
     pom:=a-ceil(sqrt(sqr(r)-sqr(i-y))+x);
     n:=n-pom;
     dec(i);
    end;
end;
procedure drugi_kvadrant;
begin
 x:=-x;
 prvi_kvadrant;
end;
procedure treci_kvadrant;
begin
 y:=-y;
 prvi_kvadrant;
end;
procedure cetvrti_kvadrant;
begin
 x:=-x;
 prvi_kvadrant;
end;
begin
 readln(x,y,r);
 n:=0;
 prvi_kvadrant;
 drugi_kvadrant;
 treci_kvadrant;
 cetvrti_kvadrant;
 if x<>trunc(x) then n:=n-(ceil(y+r)-floor(y-r));
 if y<>trunc(y) then n:=n-(ceil(x+r)-floor(x-r));
 if (x<>trunc(x)) and (y<>trunc(y)) then dec(n);
 writeln(n);
end.