#include <fstream>
#define mv 5000009
#define LL long long
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n,k,A[mv],dq[mv];
int p,u;
LL sum;
int main()
{
    f >> n >> k;
    for(int i=1; i<=n; i++) f >> A[i];

    p = 1;
    u = 0;
    for(int i=1; i<=n; i++)
    {
        while(p <= u && A[i] <= A[dq[u]]) u--;
        dq[++u] = i;
        if(dq[p] == i-k) p++;
        if(i >= k) sum += A[dq[p]];
    }

    g << sum << '\n';
    g.close();
    return 0;
}