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

int dq[5000002],a[5000002],frontt,backk;

int main()
{
    int k,n,i;
    long long suma=0;
    f>>n>>k;
    frontt=1;
    backk=0;
    for(i=1;i<=n;i++)
    {
        f>>a[i];
    }
    for(i=1;i<=n;i++)
    {
        while(frontt<=backk&&a[i]<=a[dq[backk]])
            backk--;
        backk++;
        dq[backk]=i;
        if(dq[frontt]==i-k)
            frontt++;
        if(i>=k)
            suma=suma+a[dq[frontt]];
    }
    g<<suma;
    return 0;
}