/NAMNU - Vòng tròn nam nữ

              Uses Crt;
        Var  n,m,i,d1,d2:longint; st:ansistring;
        Begin
            readln(n,m);
            readln(st);st:=st+st[1];
            for i:=1 to length(st)-1 do
            begin
                if (st[i]='0') and (st[i+1]='0') then inc(d1);
                if (st[i]='1') and (st[i+1]='1') then inc(d2);
            end;
            writeln(abs(d1-d2));
            readln;
        End.