#include <bits/stdc++.h>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
const int nmax=5e6+5;
deque<int>dq;
int a[nmax],n,k;
int main(){
    long long sum=0;
    f>>n>>k;
    for(int i=1;i<=n;++i){
      f>>a[i];
      while(!dq.empty()&&a[dq.back()]>=a[i])dq.pop_back();
      dq.push_back(i);
      if(dq.front()<=i-k)dq.pop_front();
      if(i>=k)sum+=a[dq.front()];}
    g<<sum;
}