#include <iostream>
#include <fstream>
#include <deque>

#define ll long long
#define ull unsigned long long
#define pb push_back
#define mp make_pair
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");

const int NMax = 2e5 + 5;
const int inf = 1e9 + 5;
using zint = short;

int N,K;

int main() {
    in>>N>>K;

    deque< pair<int,int> > dq;
    ll ans = 0;
    for (int i=1;i <= N;++i) {
        int val;
        in>>val;

        while (dq.size() && dq.back().first >= val) {
            dq.pop_back();
        }
        dq.push_back( mp(val,i) );

        if (dq.front().second == i-K) {
            dq.pop_front();
        }

        if (i >= K) {
            ans += dq.front().first;
        }
    }

    out<<ans<<'\n';

    in.close();out.close();
    return 0;
}