#include<cstdio>
#include<deque>
using namespace std;
int n,k,x,i;
long long s;
struct nr
{
    int nr,p;
}d;
deque<nr>c;
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",&x);
        while(!c.empty()&&c.back().nr>=x)c.pop_back();
        d.nr=x;
        d.p=i;
        c.push_back(d);
        if(c.front().p<=i-k)c.pop_front();
        if(i>=k)s=s+c.front().nr;
    }
    printf("%lld",s);
    return 0;
}