#include <iostream>
#include <fstream>

using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");

int v[6000000],d[5000000];

int main()
{
    int n,k,st=0,dr=-1;
    long long s=0;
    fin>>n>>k;
    for(int i=0;i<n;i++){
        fin>>v[i];
    }
    for(int i=0;i<n;i++){
        if(st<=dr&&d[st]==i-k){
            st++;
        }
        while(st<=dr&&v[i]<=v[d[dr]]){
            dr--;
        }
        d[++dr]=i;
        if(i>=k-1){
            s+=v[d[st]];
        }
    }
    fout<<s;
    return 0;
}