#include <bits/stdc++.h>

typedef long long ll;
using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");
const int NMAX=5000005;

int N, K, v[NMAX];
deque<int> dq;
ll sol;

int main()
{
    fin>>N>>K;
    for(int i=1;i<=N;i++)
        fin>>v[i];

    for(int i=1;i<K;i++){
        while(!dq.empty() and v[i]<=v[dq.back()])
            dq.pop_back();
        dq.push_back(i);
    }
    for(int i=K;i<=N;i++){
        while(!dq.empty() and v[i]<=v[dq.back()])
            dq.pop_back();
        dq.push_back(i);
        while(!dq.empty() and i-K+1>dq.front())
            dq.pop_front();
        sol+=v[dq.front()];
    }

    fout<<sol;

    fin.close();
    fout.close();
    return 0;
}