#include <bits/stdc++.h>
#define ll long long
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int main(){
    int n, k;
    fin >> n >> k;
    vector<int> v(n+1);
    for(int i = 1; i<=n; i++){
        fin >> v[i];
    }
    deque<int> dq;
    ll s = 0;
    for(int i = 1; i<=n; i++){
        while(!dq.empty() && v[i] < v[dq.back()])dq.pop_back();
        dq.push_back(i);
        if(dq.front() == i-k)dq.pop_front();
        if(i >= k){
            s += v[dq.front()];
        }
    }
    fout << s << '\n';

    return 0;
}