#include<cstdio>
#include<deque>
using namespace std;
int i,n,k,x;
long long s=0;
deque <int> d,p;
FILE *in,*out;
int main ()
{
    in=fopen("deque.in","r");
    out=fopen("deque.out","w");
    fscanf(in,"%d %d",&n,&k);
    for(i=1;i<=k;i++)
    {
        fscanf(in,"%d",&x);
        while(d.size()>0 && d.back()>x)
        {
            d.pop_back();
            p.pop_back();
        }
        d.push_back(x);
        p.push_back(i);
    }
    s+=d.front();
    for(i=k+1;i<=n;i++)
    {
        fscanf(in,"%d",&x);
        if(p.front()<=i-k)
        {
            d.pop_front();
            p.pop_front();
        }
        while(d.size()>0 && d.back()>x)
        {
            d.pop_back();
            p.pop_back();
        }
        d.push_back(x);
        p.push_back(i);
        s+=d.front();
    }
    fprintf(out,"%lld",s);
    return 0;
}