Uses math;
{$inline on}
Const
        finp='deque.in';
        fout='deque.out';
Type
        mat=array [1..5000000] of longint;
Var     a,stack:mat;
        n,k,f,r:longint;
        time:longint;
        res:int64;
        fi,fo:text;

Procedure Doc;      inline;
        Var i:longint;
        Begin
                Assign(fi,finp);
                Reset(fi);
                Read(fi,n,k);
                For i:=1 to n do Read(fi,a[i]);
                Close(fi);
        end;

Procedure Push(x:longint);
        Begin
                inc(r);
                stack[r]:=x;
        end;


Procedure Lam;
        Var i:longint;
        Begin
                f:=1;
                r:=0;
//                Push(1);
                For i:=1 to n do
                  Begin
                        While (f<=r) and (a[i]<=a[stack[r]]) do dec(r);
                        inc(r);
                        stack[r]:=i;
                        If stack[f]=i-k then inc(f);
                        If i>=k then res:=res+a[stack[f]];
                  end;
        end;

Procedure Inkq;                   inline;
        Begin
                Assign(fo,fout);
                Rewrite(fo);
                Write(fo,res);
                Close(fo);
        end;

        Begin
               // time:=gettickcount;
                Doc;
                Lam;
                Inkq;
               // Write((gettickcount-time)/1000);
        end.