#include <fstream>

using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int v[5000001],c[5000001];
int main()
{
    int n,k,st,dr;
    long long s=0;
    fin>>n>>k;
    st=dr=0;
    for(int i=1;i<=n;i++){
        fin>>v[i];
        if(i<k){
            while(v[i]<v[c[dr]] && st<=dr)
                dr--;
            dr++;
            c[dr]=i;
        }
        else{
            if(i-k+1>c[st])
                st++;
            while(v[i]<v[c[dr]] && st<=dr)
                dr--;
            dr++;
            c[dr]=i;
            s+=v[c[st]];
        }
    }
    fout<<s;
    return 0;
}