#include <iostream>
#include <fstream>

using namespace std;

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

int deq[5000001],l[5000001];
int N,K;

int main()
{   f>>N>>K;
    int start=0, capat=-1,i;
    long long s=0;
    for(i=0; i<N; i++)
        f>>l[i];
    for(i=0; i<N; i++)
    {
        while(start<=capat && l[i]<=l[deq[capat]])
            capat--;
        deq[++capat]=i;
        if(deq[start]==i-K)
            start++;
        if(i+1>=K)
            s+=l[deq[start]];
    }
    g<<s;

    return 0;
}