#include <bits/stdc++.h>
using namespace std;
#define pb push_back
#define fi first
#define se second
#define MOD 1000000007

typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int, int> ii;
typedef vector<ii> vii;
typedef long long ll;
typedef vector<ll> vll;
typedef vector<vll> vvll;
typedef double ld;

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


int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    
    int n, k;
    fin >> n >> k;

    deque<ii> dq;
    ll sum = 0;
    for (int i = 0; i < n; i++) {
        int x;
        fin >> x;
        while (!dq.empty() && dq.back().first > x) {
            dq.pop_back();
        }
        dq.push_back(make_pair(x, i));
        if (i - dq.front().second >= k) {
            dq.pop_front();
        }
        if (i >= k - 1)
            sum += dq.front().first;
    }
    
    fout << sum << "\n";

    return 0;
}