program alex;
var f:text;
    i,n,k,j,s,min:longint;
    a:array[1..5000000]of longint;
begin
assign(f,'deque.in');reset(f);
readln(f,n,k);
for i:=1 to n do
    readln(f,a[i]);
i:=0;
s:=0;
repeat
i:=i+1;
min:=a[i];
for j:=i+1 to i+k-1 do
    if a[j]<min then min:=a[j];
s:=s+min;
until i=n-k+1;
assign(f,'deque.out');rewrite(f);
write(f,s);
close(f);
end.