import std.conv, std.functional, std.range, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.bitmanip, std.complex, std.container, std.math, std.mathspecial, std.numeric, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; }
int readInt() { return readToken.to!int; }
long readLong() { return readToken.to!long; }
real readReal() { return readToken.to!real; }

bool chmin(T)(ref T t, in T f) { if (t > f) { t = f; return true; } else { return false; } }
bool chmax(T)(ref T t, in T f) { if (t < f) { t = f; return true; } else { return false; } }

int binarySearch(alias pred, T)(in T[] as) { int lo = -1, hi = cast(int)(as.length); for (; lo + 1 < hi; ) { const mid = (lo + hi) >> 1; (unaryFun!pred(as[mid]) ? hi : lo) = mid; } return hi; }
int lowerBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a >= val)); }
int upperBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a > val)); }



/*
  l subseqs
  x[1] < ... < x[l]
  (l - 1) (K - 1) < x[1] <= l (K - 1)
  j K - 1 <= x[j]  (2 <= j <= l)
  
  for 2 <= j <= l - 1:
    (l - 1) (K - 1) + j >= j (K - 1) + j >= j K > j K - 1
  
  (conds)
  <=>
  x[1] < ... < x[l]
  (l - 1) (K - 1) < x[1] <= l (K - 1)
  K l - 1 <= x[l]
*/

enum INF = 10L^^18;

void main() {
  try {
    for (; ; ) {
      const N = readInt();
      const K = readInt();
      auto A = new long[N];
      foreach (i; 0 .. N) {
        A[i] = readLong();
      }
      
      long ans = A[K - 1];
      
      if (K >= 2) {
        auto tailMin = new long[N + 1];
        tailMin[] = INF;
        foreach_reverse (i; 0 .. N) {
          tailMin[i] = min(A[i], tailMin[i + 1]);
        }
        
        alias Entry = Tuple!(long, "val", int, "pos");
        BinaryHeap!(Array!Entry) que;
        long sum = 0;
        int sz = 0;
        foreach_reverse (i; K .. N) {
          const l = (i + (K - 1) - 1) / (K - 1);
          assert(l >= 2);
          if (K * l <= N) {
            for (; sz > l - 1; ) {
              const e = que.front;
              que.removeFront;
              sum -= e.val;
              sz -= 1;
            }
            if (sz == l - 1) {
              long cost;
              cost += A[i];
              cost += sum;
              if (que.front.val < tailMin[K * l - 1]) {
                // none from [K l - 1, N)?
                cost -= que.front.val;
                cost += tailMin[K * l - 1];
              }
              debug {
                writefln("i = %s: l = %s, sum = %s, cost = %s", i, l, sum, cost);
              }
              chmin(ans, cost);
            }
          }
          que.insert(Entry(A[i], i));
          sum += A[i];
          sz += 1;
        }
      }
      
      writeln(ans);
    }
  } catch (EOFException e) {
  }
}