#include <bits/stdc++.h>

using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");

long long minim(deque<int> d){
    long long mini=1LL*d.back();
    d.pop_back();
    while(!d.empty()){
        if(d.back()<mini)
            mini=1LL*d.back();
        d.pop_back();
    }
    return mini;
}
/*
void Afisare(deque<int> d){
    cout<<"Sir: ";
    cout<<endl;
    while(!d.empty()){
        cout<<d.front()<<" ";
        d.pop_front();
    }
    cout<<endl;
}
*/
int main()
{
    long long n,k,s=0,x,nr=0;
    deque<int> d;
    fin>>n>>k;
    while(nr<n){
        fin>>x;
        d.push_back(x);
        if(nr>=k-1){
            if(nr>=k)
                d.pop_front();
            //Afisare(d);
            //cout<<"Minim: \n";
            s+=1LL*minim(d);
            //cout<<minim(d);
            //cout<<endl<<endl;
        }
        nr++;
    }
    fout<<s;
    return 0;
}