#include <iostream>
#include <fstream>
using namespace std;

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

int dq[5000001], x[5000001];
int n,k,i,f, b;
long long sum;

int main()
{
    f=1; b=0;
    fin>>n>>k;
    for(i=1; i<=n; i++){
        fin>>x[i];
    }

    for(i=1; i<=n; i++){
        while(f<=b and x[i]<=x[dq[b]]) b--;
        b++;
        dq[b]=i;

        if(dq[f]==i-k) f++;

        if(i>=k) sum+=x[dq[f]];
    }
    fout<<sum;
    return 0;
}