#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");

const int N = 5000001;
int d[N],v[N];


int main()
{
    int st=0, dr=-1,n,k,sum=0;
    fin>>n>>k;
    for(int i=0; i<n; i++)
    {
         fin>>v[i];
         if(st<=dr&&d[st]==i-k)
           st++;
         while(st<=dr&&v[i]<=v[d[dr]])
          dr--;
        d[++dr]=i;
        if(i>=k-1) sum+=v[d[st]];
    }
    fout<<sum;
    return 0;
}