#include <stdio.h>
#define maxn 5000010
int N, K;
int A[maxn], Deque[maxn];
int Front, Back;
long long Sum;
int main()
{
freopen("deque.in", "r", stdin);
freopen("deque.out", "w", stdout);
int i;
scanf("%d %d ", &N, &K);
for (i = 1; i <= N; i++) 
scanf("%d ", &A[i]);
Front = 1, Back = 0; // Initializare, Back < Front => deque-ul este vid
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) Sum += A[ Deque[Front]];     
}
printf("%lld\n", Sum);
return 0;
}