#include <fstream>
#include<deque>
#include<algorithm>
using namespace std;
deque<long int > csec;
int main()
{
    ifstream f("deque.in");
    ofstream g("deque.out");
    long  i,n,k,x,s=0,min=10000001,first;
    f>>n>>k;
    for(i=1;i<=k;i++)
    {
        f>>x;
        csec.push_back(x);
        if(x<min)
            min=x;
    }
    s=min;
    for(i=k+1;i<=n;i++)
    {
        f>>x;
        first=csec.front();
        csec.pop_front();
        csec.push_back(x);
        if(min==first)
            min=*min_element(csec.begin(),csec.end());
        else
            if(x<min)
                min=x;
        s+=min;

    }
    g<<s;
    f.close();
    g.close();
    return 0;
}