#include <bits/stdc++.h>
#define debug(x) cerr << #x << " " << x << " ";
#define debugs(x) cerr << #x << " " << x<< '\n';

using namespace std;

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

const int NMAX = 5000007;

deque <int> dq;
int v[NMAX];

int main()
{
    int n, k;
    long long s=0;
    in>>n>>k;
    for(int i=0; i<n; i++)
    {
        in>>v[i];
        if(dq.size() && dq.front()==i-k)
        {
            dq.pop_front();
        }
        while(dq.size() && v[dq.back()] >= v[i])
        {
            dq.pop_back();
        }
        dq.push_back(i);
        if(i>=k-1)
            s+=v[dq.front()];
    }
    out<<s;
    return 0;
}