#include <iostream>
#include <fstream>

using namespace std;

ifstream in("deque.in");
ofstream out("deque.out");

const int N=5000000;

int dq[N], v[N];

int main()
{
    int n, k, s=0, st=0, dr=-1;
    in>>n>>k;
    for(int i=0; i<n; i++){
        in>>v[i];
    }
    for(int i=0; i<n; i++){
        if(st<=dr && dq[st]==i-k){
            st++;
        }
        while(st<=dr && v[i]<=v[dq[dr]]){
            dr--;
        }
        dq[++dr]=i;
        if(i>=k-1){
            s+=v[dq[st]];
        }
    }
    out<<s;
    return 0;
}