#include <iostream>
#include <deque>
#include <vector>
#include <cstring>
#include <bitset>
#include <algorithm>
#define INF 1000010
#define uint unsigned int
#define ll long long
using namespace std;

deque<pair<int,int> > Q;

int N, K, i, A[5000010], x;
ll sol;


int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    scanf("%d%d", &N, &K);
    for(i=1;i<=N;i++)
        scanf("%d", &A[i]);
    for(i = 1; i < K; i++)
    {
        while(!Q.empty())
        {
            x = Q.back().first;
            if(x >= A[i])
                Q.pop_back();
            else
                break;
        }
        Q.push_back(make_pair(A[i], i));
    }
    for(; i <= N; i++)
    {
        while(!Q.empty())
        {
            x = Q.front().second;
            if(x <= i - K)
                Q.pop_front();
            else
                break;
        }
        while(!Q.empty())
        {
            x = Q.back().first;
            if(x >= A[i])
                Q.pop_back();
            else
                break;
        }
        Q.push_back(make_pair(A[i], i));
        sol = sol + Q.front().first;
    }
    printf("%lld\n",sol);
    return 0;
}