#include <fstream>
#include <deque>
#define MAXN 5000041
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");

deque <int> D;
int N,k,a[MAXN];
long long S;

int main(){

    in >> N >> k;
    for(int i=1; i <= N; ++i) in >> a[i];
    for(int i=1; i <= N; ++i)
        if(i<k){
            while(!D.empty()&& a[i]<=a[D.back()]) D.pop_back();
            D.push_back(i);
        }
        else{
            while(!D.empty()&&a[i]<=a[D.back()])  D.pop_back();
            D.push_back(i);
            if(D.front()<=i-k) D.pop_front();
            S+=a[D.front()];
        }
    out << S;

    return 0;
}