#include <bits/stdc++.h>
using namespace std;

const int N = 5e6+5;
typedef long long ll;

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

ll v[N];

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

    deque<ll> dq;
    ll s=0;

    for(int i=1; i<=n; i++)
    {
        in>>v[i];
        while(!dq.empty() && v[dq.back()] >= v[i]) dq.pop_back();

        dq.push_back(i);
        if(dq.front() <= i-k) dq.pop_front();
        if(i >=k) s+=v[dq.front()];
    }

    out<<s;
}