#include <bits/stdc++.h>
#define fr(i,n) for(int i=0;i<n;i++)
#define int long long
#define i first
#define v second
using namespace std;

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

int n,k;

deque<pair<int,int> > q;

int32_t main()
{
    f>>n>>k;
    int s=0;
    int nr;
    fr(i,n)
    {
        f>>nr;
        if(!q.empty()&&q.front().i==i-k) q.pop_front();
        while(!q.empty()&&q.back().v>nr) q.pop_back();
        q.push_back({i,nr});
        if(i>=k-1)s+=q.front().v;
        //g<<s<<'\n';
    }
    g<<s;
    return 0;
}