#include<fstream>
#include<deque>

using namespace std;


int main(){
    int ssum=0,n,k;
    int * A=new int[5000000];
    deque<int> doubleq;
    ifstream cin("deque.in");
    ofstream cout("deque.out");
    cin>>n>>k;
    for( int i=0;i<n;i++){
        cin>>A[i];
        if(doubleq.size()&&doubleq.front()==i-k){
            doubleq.pop_front();
        }
        while(doubleq.size()&&A[doubleq.back()]>A[i]){
            doubleq.pop_back();
        }
        doubleq.push_back(i);
        if(i>k-2){
            ssum+=A[doubleq.front()];
        }
        
    }
    cout<<ssum;
}