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

int n,k,st,dr,v[5000000],dq[5000000];
long long s;

int main()
{

    in>>n>>k;
    for(int i=0;i<n;i++)
        in>>v[i];
    st=0;dr=-1;
    for(int i=0;i<n;i++){
        if(st<=dr && dq[st]==i-k){
            st++;
        }
        while(st<=dr && v[i]<=v[dq[dr]])
            dr--;
        dq[++dr]=i;
        if(i>=k-1){
            s+=v[dq[st]];
        }
    }
    out<<s;
    return 0;
}