#include <stdio.h>

#define BUF 1 << 17
char buf[BUF];
int pos = BUF;

inline char next()  {
    if(pos == BUF)
        fread(buf, 1, BUF, fin), pos = 0;
    return buf[pos++];
}

inline int get_int()  {
    int x = 0, semn = 1;
    char ch = next();
    while(!isdigit(ch) && ch != '-')
        ch = next();
    if(ch == '-')
        ch = next(), semn = -1;
    while(isdigit(ch))
        x = x * 10 + ch - '0', ch = next();
    return x * semn;
}

int main()
{
    int N, K, v[5000001], deque[5000001], front = 1, back = 0;

    long long sum = 0;

    freopen("deque.in", "r", stdin);
    //freopen("deque.out", "w", stdout);

    fread(buffer, 1, 45000000, stdin);

    N = get_int(); K = get_int();

    for(int i = 1; i <= N; i++)
    {
        v[i] = get_int();
    }

    for(int i = 1; i < K; i++)
    {
        while(front <= back && v[i] <= v[deque[back]])
        {
            back--;
        }

        deque[++back] = i;
    }


    for(int i = K; i <= N; i++)
    {
        while(front <= back && v[i] <= v[deque[back]])
        {
            back--;
        }

        deque[++back] = i;

        if(deque[front] == i - K) front++;

        sum += v[deque[front]];
    }

    printf("%lld", sum);

    return 0;
}