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

/*double exp(double x)
{
    double sum = 0, act = x, k = 3.667;
    for(double i = 1; i<=6; i++)
    {
        sum += (i - k) * act;
        act *= x;
    }

    return sum;
}

double bs()
{
    double lo = 0.0, hi = 5.0, mid;
    while(hi - lo>0.001)
    {
        mid = (hi + lo) / 2;

        if(exp(mid)<0.001 && exp(mid)>0.001)
            return mid;

        if(exp(mid)>0)
            hi = mid;
        else
            lo = mid;
    }

    return mid;
}

int main()
{
    //cout<<bs()<<'\n';

    int rasp = 0;
    for(int i = 100; i<1000; i++)
    {
        if(i%21==0)
        {
            if(i%10!=i/100)
                rasp++;
            else
                cout<<i<<'\n';
        }
    }
    cout<<rasp<<'\n';

    return 0;
}*/


long long  n, v[5000000], p=1, q, k, s;
int d[5000000];

int main()
{
    in>>n>>k;
    for(int i = 0; i<n; i++)
    {
        in>>v[i];
        while(v[d[q]]>=v[i] && q>=p)
            q--;

        d[++q] = i;

        if(i-d[p]>=k)
            p++;

        if(i>=k-1)
        s+=v[d[p]];
    }

    out<<s<<'\n';
    return 0;
}