#include <fstream>
#include <deque>
#define MAXN 5000005
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");

long n,k,v[MAXN];
long long S;
deque<long> dq;

int main()
{
    long i;
    f>>n>>k;
    for(i=1;i<=n;i++)
        f>>v[i];
    for(i=1;i<k;i++){
        while(!dq.empty()&&v[i]<v[dq.back()])
            dq.pop_back();
        dq.push_back(i);}
    for(i=k;i<=n;i++){
        while(!dq.empty()&&dq.front()<i-k+1)
            dq.pop_front();
        while(!dq.empty()&&v[i]<v[dq.back()])
            dq.pop_back();
        dq.push_back(i);
        S+=v[dq.front()];}
    g<<S<<'\n';
    f.close();
    g.close();
    return 0;
}