#include<stdio.h>
#include<deque>
using namespace std;

deque<int> v;
deque<int> p;

int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    int n,k,x,i,j;
    long long s;

    scanf("%d%d",&n,&k);
    for(i=1;i<=k;++i)
    {
        scanf("%d",&x);
        while(!v.empty()&&x<v.back())
        {
            p.pop_back();
            v.pop_back();
        }
        p.push_back(i);
        v.push_back(x);
    }
    s=v.front();
    for(i=k+1;i<=n;++i)
    {
        scanf("%d",&x);
        while(!v.empty()&&x<v.back())
        {
            p.pop_back();
            v.pop_back();
        }
        if(!v.empty()&&p.front()==i-k)
        {
            p.pop_front();
            v.pop_front();
        }
        p.push_back(i);
        v.push_back(x);
        s+=v.front();
    }
    printf("%lld\n",s);
    return 0;
}