#include <bits/stdc++.h>
#define fastio ios_base::sync_with_stdio(NULL),cin.tie(NULL),cout.tie(NULL);
#define pb push_back
#define mp make_pair
#define ll long long
#define ull unsigned long long
#define MAX 100000
#define FILES freopen("deque.in","r",stdin);\
              freopen("deque.out","w",stdout);
#define mod 666013
#define int ll
using namespace std;
int n,m,s,a;
deque<pair<int,int>>dq;
signed main()
{
    fastio
    FILES
    cin >> n >> m;
    for(int i = 1;i <= m; ++i)
    {
        cin >> a;
        while(!dq.empty() && dq.back().first >= a)
            dq.pop_back();
        dq.push_back(mp(a,i));
    }
    for(int i = m + 1;i <= n; ++i)
    {
        cin >> a;
        s += dq.front().first;
        while(!dq.empty() && dq.back().first >= a)
        dq.pop_back();
        while(!dq.empty() && dq.front().second <= i - m) dq.pop_front();
        dq.push_back(mp(a,i));
    }
    s += dq.front().first;
    cout << s;
}