#include <fstream>

using namespace std;

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

int const N=5000001;
int v[N], d[N];

int main()
{
    int st=0, dr=-1, n, k;
    long long s=0;
    in>>n>>k;
    for(int i=0; i<n; i++)
    {
        in>>v[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]];
    }
    out<<s;
    return 0;
}