#include<fstream>
using namespace std;
long long s,k,st=-1,dr,v[5000001],d[5000001],n;
inline void dreapta(int i) {
    while(st<=dr&&v[i]<=v[d[dr]])
        dr--;
    d[++dr] = i;
}
inline void stanga(int i) {
    if(d[st]==i-k) {
        st++;
    }
}
int main()
{
    ifstream q("deque.in");
    ofstream w("deque.out");
    q>>n>>k;
    for(int i=1;i<=n;i++)
    {
        q>>v[i];
    }
    for(int i=1;i<=n;i++)
    {
        if(i>k)
            stanga(i);
        dreapta(i);
        //w << i << " -> " << v[d[st]] << "\n";
        if(i>=k) s+=v[d[st]];
    }
    w<<s;
}