#include <bits/stdc++.h>

using namespace std;

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

int main()
{
    int n, a, k;
    long long int suma=0;
    fin>>n>>k;
    deque<pair<int, int>> v;
    for(int i=0; i<n; i++)
    {
        fin>>a;
        ///front este minim
        while(!v.empty() && v.back().first > a)
            v.pop_back();
        v.emplace_back(a, i);
        if(v.front().second + k == i)
            v.pop_front();
        if(i>=k-1)
            suma+=v.front().first;
    }
    fout<<suma;
    return 0;
}