#include <bits/stdc++.h>

using namespace std;

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

int main(){
    int n,k;
    fin >> n >> k;

    deque<int> dq;
    vector<int> A(n);
    for(int i = 0;i < n; ++i)
        fin >> A[i];

    long long sum = 0;
    for(int i = 0;i < n; ++i){
        if(!dq.empty() && dq.front() == i - k)
            dq.pop_front();

        while(!dq.empty() && A[dq.back()] >= A[i])
            dq.pop_back();

        dq.push_back(i);

        if(i >= k-1)
            sum += A[dq.front()];
    }
    fout << sum;
    return 0;
}


//dq = {-1 }