#include<bits/stdc++.h>

using namespace std;

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

long long s;
int n,i,x,k,A[5000001];
deque<int>Q;

void solve(){
    fin>>n>>k;
    for(int i=1;i<=n;i++) fin>>A[i];
    for(int i=1;i<=n;i++){
     while(!Q.empty()&&A[i]<=A[Q.back()]) Q.pop_back();
     Q.push_back(i);
     if(Q.front()==i-k) Q.pop_front();
     if(i>=k) s+=A[Q.front()];
    }
    fout<<s;
}

int main(){
   solve();
    return 0;
}