#include<cstdio>
int s,d,n,k,dq[5000001],v[5000001];
long long sum;
inline void st(int i)
{
    if(i-dq[s]==k)
        ++s;
}
void dr(int i)
{
    while(s<=d && v[dq[d]]>=v[i])
        --d;
    dq[++d]=i;
}
int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    scanf("%d%d",&n,&k);
    for(int i=1;i<=n;++i)
        scanf("%d",&v[i]);
    dq[1]=1;
    s=d=1;
    for(int i=2;i<=k;i++)
    {
        st(i);
        dr(i);
    }
    sum+=v[dq[s]];
    for(int i=k+1;i<=n;i++)
    {
        st(i);
        dr(i);
        sum+=v[dq[s]];
    }
    printf("%lld",sum);
    return 0;
}