#include<iostream>
#include<fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
long v[5000000],u[5000000];
int main()
{
    ifstream f("deque.in");
    ofstream g("deque.out");
    int n,k,i,s,d;
    long long x=0;
    f>>n>>k;
    for(i=1;i<=n;i++)
        f>>v[i];
    s=1,d=0;
    for(i=1;i<=n;i++)
    {
        while(s<=d && v[i]<=v[u[d]])
            d--;
        u[++d]=i;
        if(u[d]==i-k)
            s++;
        if(i>=k)
            x=x+v[u[s]];
    }
    g<<x;
    return 0;
}