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

long long n, k, dr=-1, st, s;
int v[5000001], d[5000001];
ifstream in("deque.in");
ofstream out("deque.out");
int main()
{
    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;
}