#include <bits/stdc++.h>

using namespace std;
//www.infoarena.ro/problema/deque
ifstream in("deque.in");
ofstream out("deque.out");
deque <long long> D;
#define MAX 5000008
long long v[MAX];
int main()
{
    long long n,k,sum=0;
    in>>n>>k;
    for(int i=1;i<=n;i++)
     in>>v[i];
     for(int i=1;i<=n;i++)
     {
         while(!D.empty()&&v[D.back()]>v[i])
             D.pop_back();
          D.push_back(i);
          if(D.front()==i-k)D.pop_front();
          if(i>=k)sum+=v[D.front()];
     }
     out<<sum;
    return 0;
}