#include <iostream>
#include <fstream>
using namespace std;
int Deq[5000001],poz[5000001];
ifstream f("deque.in");
ofstream g("deque.out");
int main(){
    int n,k;
    f>>n>>k;
    int fr=0, bk=-1;
    long long sum=0;
    for(int i=0;i<n;++i){
        f>>Deq[i];
       if(fr<=bk && poz[fr]==i-k)
           ++fr;
       while(fr<=bk&&Deq[i]<=Deq[poz[bk]])
            --bk;
        poz[++bk]=i;
        if(i>=k-1)
            sum+=Deq[poz[fr]];
    }
    g << sum ;
    return 0;
}