#include <stdio.h>

#define nmax 5000005

int n, k;
long long int sum;
int a[nmax], deque[nmax], i, j;
int first = 1, last = 0, aux, semn = 1;
char nr[20];

int main()
{
    FILE *in, *out;
    in  = fopen("deque.in", "r");
    out = fopen("deque.out", "w");
    
    fscanf(in, "%d %d", &n, &k);
    fgets(nr, 20, in);
    
    for (i = 1; i <= n; i++)
    {
        j = 0;
        fgets(nr, 20, in);
        if (nr[0] == '-')
            j = 1;
        while (nr[j] >= '0' && nr[j] <= '9')
            a[i] = a[i]*10 + nr[j++] - '0';
        a[i] *= (nr[0] == '-' ? -1 : 1);
        
        while(first <= last && a[i] <= a[deque[last]])
            last--;
        deque[++last] = i;
        if (i - deque[first] == k)
            first++;
        if (i >= k)
            sum += a[deque[first]];
    }
    fprintf(out, "%lld\n", sum);
}