#include<cstdio>
#include<deque>
using namespace std;
int n,k,v[5000001];
long long s=0;
deque <int> d,p;
int main (){
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    scanf("%d %d",&n,&k);
    for(int i=1;i<=k;i++)
    {
        scanf("%d",&v[i]);
        while(d.size()>0 and d.back()>v[i])
        {
            d.pop_back();
            p.pop_back();
        }
        d.push_back(v[i]);
        p.push_back(i);
    }
    s+=d.front();
    for(int i=k+1;i<=n;i++)
    {
        scanf("%d",&v[i]);
        if(p.front()<=i-k)
        {
            d.pop_front();
            p.pop_front();
        }
        while(d.size()>0 and d.back()>v[i])
        {
            d.pop_back();
            p.pop_back();
        }
        d.push_back(v[i]);
        p.push_back(i);
        s+=d.front();
    }
    printf("%lld",s);
    return 0;
}