#include <iostream>
#include<fstream>

using namespace std;


long long v[50000010];
int deq[5000010];

int main()
{

    ifstream in;
    in.open("deque.in");
    ofstream out;
    out.open("deque.out");
    int n,k ,start=1 , sfarsit=0;
    long long suma = 0;
    in>>n;
    in>>k;
    for(int i=0;i<n;i++)
    {
        in>>v[i];
        while(start <= sfarsit && v[i]<=v[deq[sfarsit]])
            sfarsit--;
        sfarsit++;
        deq[sfarsit] = i;
        if(deq[start] < i-k+1)
            start++;
        if(i>=k-1)
        suma = suma + v[deq[start]];
   //     cout<<suma<<endl;


    }

    out<<suma;

    return 0;
}