#include <bits/stdc++.h>
#define nMax 10000001
using namespace std;

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

deque <int> q;
int main(){
    int n,k;f>>n>>k;
    int x,s=0;
    vector <int> v;
    for(int i=0;i<n;++i) {f>>x;v.push_back(x);}
    for(int i=0;i<n;++i){
            while(!q.empty()&&v[i]<=v[q.back()]) q.pop_back();
    q.push_back(i);
    if(q.front()==i-k) q.pop_front();
    if(i>=k-1) s+=v[q.front()];
    }
    g<<s;
}