#include <iostream>
#include <cstdio>
#include <vector>
#include <deque>
#define NMAX 5000005

using namespace std;

vector <int> dQ;
vector <int>::iterator st, dr;
deque <int> dq;
int n, k, v[NMAX];
long long sum;

void read()
{
    scanf("%d%d", &n, &k);
    for(int i=0; i<n; ++i)
    {
        scanf("%d", &v[i]);
    }
}

void solve()
{
    dQ.push_back(0);
    st = dQ.begin();
    dr = dQ.end();
    for(int i=1; i<n; ++i)
    {
        while(st < dr && v[dQ.back()] >= v[i])
        {
            dr--;
            dQ.pop_back();
        }
        dQ.push_back(i);
        dr = dQ.end();
        if(*st < i-k+1)
            st++;
        if(i >= k-1)
            sum += v[*st];
    }

}

void solve2()
{
    for(int i=0; i<n; ++i)
    {
        while(!dq.empty() && v[dq.back()] >= v[i])
        {
            dq.pop_back();
        }
        dq.push_back(i);
        if(dq.front() < i-k+1)
            dq.pop_front();
        if(i >= k-1)
            sum += v[dq.front()];
    }
}

int main()
{
    freopen("deque.in", "r", stdin);
    freopen("deque.out", "w", stdout);
    read();
    solve2();
    printf("%lld", sum);
    return 0;
}