#include <fstream>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
long long s;
int n,k,a[5000004],c[5000004],pr,i,ul;
int main()
{
    fin>>n>>k;
    for(i=1;i<=n;i++)
    {
        fin>>a[i];
    }
    pr=1;
    ul=0;
    /*for(i=1;i<=k;i++)
    {
        while(pr<=ul && a[c[ul]]>=a[i])
        {
            ul--;
        }
        ul++;
        c[ul]=i;
        if(c[pr]<i-k+1)
        {
            pr++;
        }
    }
    s=s+a[c[pr]];
    */
    for(i=1;i<=n;i++)
    {
        while(pr<=ul && a[c[ul]]>=a[i])
        {
            ul--;
        }
        ul++;
        c[ul]=i;
        if(c[pr]<i-k+1)
        {
            pr++;
        }
        if(i>=k) s=s+a[c[pr]];
    }
    fout<<s;
    return 0;
}