#include <cstdio>
#include <deque>

#define LIM_MAX 5000000
using namespace std;

int myArray[LIM_MAX];

int main()
{
    FILE* in = freopen("deque.in", "r", stdin);
    FILE* out = freopen("deque.out", "w", stdout);

    long long int i;
    long long int N;
    long long int K;
    long long int S = 0;
    deque<long long int> myDeque;

    scanf("%lld %lld", &N, &K);
    for (i = 1; i <= N; ++i)
        scanf("%lld", &myArray[i]);
    fclose(in);

    for (i = 1; i <= N; ++i)
    {
        while (!myDeque.empty() && myArray[myDeque.back()] >= myArray[i])
            myDeque.pop_back();

        myDeque.push_back(i);

        if (myDeque.front() == i - K)
            myDeque.pop_front();

        if (i >= K)
            S += myArray[myDeque.front()];
    }

    printf("%lld", S);
    fclose(out);

    return 0;
}