#include <cstdio>
#include <deque>

using namespace std;

const int MAX_N = 5000000;

FILE *in, *out;

deque<int> dq;

int v[MAX_N];

int main()
{
    in = fopen("deque.in","r");
    out = fopen("deque.out", "w");
    int n, k;
    int i;
    int sum;
    fscanf(in, "%d%d", &n, &k);
    for(i = 0; i < n; i++)
        fscanf(in, "%d", &v[i]);
    i = 0;
    while(i < k)
    {
        while((!dq.empty()) && (v[dq.back()] > v[i])) dq.pop_back();
        dq.push_back(i);
        i++;
    }
    sum = v[dq.front()];
    for(int i = k; i < n; i++)
    {
        if((!dq.empty()) && (dq.front() <= i-k)) dq.pop_front();
        while((!dq.empty()) && (v[dq.back()] > v[i])) dq.pop_back();
        dq.push_back(i);
        sum += v[dq.front()];
    }
    fprintf(out, "%d", sum);
    fclose(in);
    fclose(out);
    return 0;
}