#include <fstream>
#include <deque>
#define ind first
#define val second
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
deque <pair<int,int> > v;
int n,k,x,i,s;
int main(){
    fin>>n>>k;
    for(i=1;i<=n;i++){
        fin>>x;
        while(v.size() && x<v.back().val)
            v.pop_back();
        v.push_back(make_pair(i,x));
        if(i-v.front().ind==k)
            v.pop_front();
        if(i>=k) s+=v.front().val;
    }
    fout<<s;
    return 0;
}