#include <cstdio>
#include <deque>
#include <iostream>
using namespace std;

int n,k;
long long s;
deque <int>v;
deque <int>p;
int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    scanf("%d %d\n",&n,&k);
    for(int i=1;i<=k;i++)
    {
        int x;
        scanf("%d\n",&x);
        while(!v.empty()&&x<v.back())
        {
            p.pop_back();
            v.pop_back();
        }
        v.push_back(x);
        p.push_back(i);
    }
    s+=v.front();
    for(int i=k+1;i<=n;i++)
    {
        int x;
        scanf("%d\n",&x);
        if(p.front()<=i-k)
        {
            v.pop_front();
            p.pop_front();
        }
        while(!v.empty()&&x<v.back())
        {
            v.pop_back();
            p.pop_back();
        }
        v.push_back(x);
        p.push_back(i);
        s+=v.front();
    }
    printf("%lld\n",s);
    return 0;
}