#include<bits/stdc++.h>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int N,K,v[5000101],Front,Back,Deque[5000101];
long long s;
int main()
{
    f>>N>>K;
    for(int i=1;i<=N;++i)f>>v[i];
    Front=1,Back=0;
    for(int i=1;i<=N;++i){
        while(Front<=Back&&v[i]<=v[Deque[Back]])--Back;
        Deque[++Back]=i;
        if(i-K==Deque[Front])++Front;
        if(K<=i)s+=v[Deque[Front]];
    }
    g<<s;
    return 0;
}