#include <iostream>
#include <fstream>
#include <deque>
#define ll long long
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
 int n,k,v[5000005],st,dr;
 deque <int> q;
 ll sol;
int main()
{ int i,j,x;
    f>>n>>k;
     st=1; dr=0;

    for(i=1;i<=n;i++)
    { f>>v[i];

      while(!q.empty() && v[i]<=v[q.back()])
       q.pop_back();

      while(!q.empty() && q.front()<i-k+1)
       q.pop_front();

       q.push_back(i);

         if (i>=k) sol+=v[q.front()];

    }
    g<<sol<<"\n";
    return 0;
}