#include <fstream>
#define N 5000005
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");

int a[N], d[N];

int n, k;

int pr, ul;

int main()
{
    int i;
    long long s = 0;
    fin >> n >> k;
    for(i = 1; i <= n; ++ i)
        fin >> a[i];
    pr = 1; ul = 0;
    for(i = 1; i <= n; ++ i)
    {
        while(pr <= ul && a[i] <= d[ul])
            ul --;
        d[++ul] = a[i];
        if(d[pr] == a[i-k])
            pr ++;
        if(i >= k)
            s += 1LL*d[pr];
    }
    fout << s;
    return 0;
}