#include<stdio.h>

#define MAXN 5000015

using namespace std;

int A[MAXN], deque[MAXN], i , j , N , back , front, k;
long long int S;

int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    
    scanf("%d %d",&N ,&k);
    
    for( i = 1; i <= N ; i++)
         scanf("%d", &A[i]);
         
    
    back = 0; front = 1;
    
    for( i = 1; i <= N ; i++)
    {
         while(front <= back && A[i] <= A[deque[back]] ) back --;
         
         deque[++back] = i;
         
         if(deque[front] == i - k) front ++;
         
         if( i >= k ) S += A[deque[front]];
    }
    
    printf("%lld",S);
    
    return 0;
}