#include <cstdio>
#define maxn 500001

long int sum=0;
int i,n,k,st=1,dr=0,deq[maxn],v[maxn];

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 ", &v[i]);
        while(dr>=st && v[i]<=v[deq[dr]])
            dr--;
        dr++;
        deq[dr]=i;
        if(deq[st]==i-k)
            st++;
        if(i>=k)
            sum+=v[deq[st]];
    }
    printf("%lld", sum);
    return 0;
}