#include<fstream>
using namespace std;
int x[5000002],v[5000002];

int main()
{
    ifstream f("deque.in");
    ofstream g("deque.out");

    int i,j=1,n,z=0,k;
    long long int s=0;

    f>>n>>k;

    for(i=1; i<k; ++i)
    {
        f>>x[i];

        if(v[j]==i-k)
            j++;

        while(j<=z && x[i]<=x[v[z]])
            z--;

        v[++z]=i;
    }

    for(i=k; i<=n; ++i)
    {
        f>>x[i];

        if(v[j]==i-k)
            j++;

        while(j<=z && x[i]<=x[v[z]])
            z--;

        v[++z]=i;

        s=s+x[v[j]];
    }

    g<<s;
}