#include <fstream>
#include <deque>
using namespace std;
 ifstream fin("deque.in");
 ofstream fout("deque.out");
 deque <long long> d;
 #define nmax 5000005
long long k,n,i,a[nmax],m[nmax],s=0,j;
int main()
{
    fin>>n>>k;
    for(i=1;i<=n;i++)
    {
        fin>>a[i];
        while ((!d.empty()) && (a[d.back()]>a[i]))
            d.pop_back();
        d.push_back(i);
        if(i>=k)
        {
            if(d.front()<i-k+1)
                d.pop_front();
            m[i]=a[d.front()];
        }
    }
    for(i=k;i<=n;i++)
    {
        s+=m[i];
    }
    fout<<s;
    return 0;
}