#include <stdio.h>
#include <ctype.h>

#define BUFFER_SIZE 1 << 17

char buffer[BUFFER_SIZE];

int p = BUFFER_SIZE;

inline char next()
{
    if(p == BUFFER_SIZE) fread(buffer, 1, BUFFER_SIZE, stdin), p = 0;

    return buffer[p++];
}

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], d[5000001], f = 1, b = 0;

    long long sum = 0;

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

    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(f <= b && v[i] <= v[d[b]])
        {
            b--;
        }

        d[++b] = i;
    }


    for(int i = K; i <= N; i++)
    {
        while(f <= b && v[i] <= v[d[b]])
        {
            b--;
        }

        d[++b] = i;

        if(d[f] == i - K) f++;

        sum += v[d[f]];
    }

    printf("%lld", sum);

    return 0;
}