#include <iostream>
#include <fstream>
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
int n, k, v[5000005], c[5000005], f, s;
long long sum;
int main()
{
    in >> n >> k;
    for(int i = 1; i <= n; i++)
        in >> v[i];
    f = 1, s = 0;
    for(int i = 1; i <= n; i++){
        while(f <= s && v[i] <= v[c[s]])
            s--;
        c[++s] = i;

        if(c[f] == i-k)
            f++;
        if(i >= k)
            sum += v[c[f]];
    }
    out << sum;
    return 0;
}