#include <bits/stdc++.h>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
deque <pair<long long,int> > dq;
int main()
{
    int n,i,k;
    long long x,s = 0;
    fin >> n >> k;
    for(i = 1; i <= n; i++){
        fin >> x;
        while(!dq.empty() && x <= dq.back().first) dq.pop_back();
        dq.push_back({x,i});
        while(!dq.empty() && dq.front().second <= i - k) dq.pop_front();
        if(i >= k) s += dq.front().first;
    }
    fout << s;
    return 0;
}