///just experimenting :D

#include <stdio.h>
#include <deque>

#define BUFFER_SIZE 125000

int p = 0; char buffer[BUFFER_SIZE];

__attribute__((always_inline)) int read()
{
    int number = 0; char sign = '+';

    while(buffer[p] < '0')
    {
        sign = buffer[p];

        if(++p == BUFFER_SIZE)
        {
           fread(buffer, 1, BUFFER_SIZE, stdin);

           p = 0;
        }
    }

    while(buffer[p] > '/')
    {
        number = number * 10 + buffer[p] - 48;

        if(++p == BUFFER_SIZE)
        {
           fread(buffer, 1, BUFFER_SIZE, stdin);

           p = 0;
        }
    }

    if(sign == '-') number = -number;

    return number;
}

FILE *fin = fopen("deque.in", "r");
FILE *fout = fopen("deque.out", "w");

#define MAXN 5000001

std::deque <int> q;

int N, K;
int v[MAXN];long long sum;

int main()  {
    N = read(), K = read();
    for(int i = 1;i <= N;i++)  {
        v[i] = read();
    }
    for(int i = 1;i <= N;i++)  {
        while(!q.empty() && v[i] <= v[q.back()])
            q.pop_back();
        q.push_back(i);
        if(q.front() == i - K)
            q.pop_front();
        if(i >= K)
            sum += 1LL * v[q.front()];
    }
    fprintf(fout, "%lld", sum);
    fclose(fin);
    fclose(fout);
    return 0;
}