#include <fstream>
#define DIM 5000001
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n,k,i,p,u,v[DIM],d[DIM];
long long sol;
int main() {
    fin>>n>>k;
    for (i=1;i<=n;i++)
        fin>>v[i];
    u=0;
    p=1;
    sol=0;
    for (i=1;i<=n;i++) {
        while (u>=p && v[i]<=v[d[u]])
            u--;
        d[++u]=i;
        if (i-d[p]+1>k)
            p++;
        if (i>=k)
            sol+=v[d[p]];
    }
    fout<<sol;
    return 0;
}