#include <iostream>
#include <fstream>

using namespace std;

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

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

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