#include <stdio.h>
#include <deque>
using namespace std;
FILE*fin = fopen("deque.in", "r");
FILE*fout = fopen("deque.out", "w");

#define NMax 5000001
deque<int> Min;
int n, k, v[NMax];
unsigned long long S;

int main()
{
    int i;

    fscanf(fin, "%d %d", &n, &k);
    for(i = 1; i <= n; i++)
        fscanf(fin, "%d", &v[i]);

    for(i = 1; i <= k; i++) {
        while(!Min.empty() && v[i] <= v[Min.back()])
            Min.pop_back();
        Min.push_back(i);
    }
    S += v[Min.front()];

    for(i = k + 1; i <= n; i++) {
        if(Min.front() <= i - k)
            Min.pop_front();
        while(!Min.empty() && v[i] <= v[Min.back()])
            Min.pop_back();
        Min.push_back(i);
        S += v[Min.front()];
    }

    fprintf(fout, "%d\n", S);
    return 0;
}