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

const int N=5000001;

int v[N];
int d[N];

ifstream in("deque.in");
ofstream out("deque.out");
int main()
{
    int n, k, i, st, dr;
    long long s;
    in>>n >>k;
    st=0;
    dr=-1;
    s=0;
    for(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;
}