#include <stdio.h>

#define nmax 5000005

int n, k;
long long int sum;
int a[nmax], deque[nmax], i;
int first = 1, last = 0;

int main()
{
    FILE *in, *out;
    in  = fopen("deque.in", "r");
    out = fopen("deque.out", "w");
    
    fscanf(in, "%d %d", &n, &k);
    
    for (i = 1; i <= n; i++)
    {
        fscanf(in, "%d", &a[i]);
        
        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);
}