#include <bits/stdc++.h>
using namespace std;

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

long long int n, k, suma, nr, i, w, minn, inceput;
deque<long long int> dq;

int main()
{
    ios::sync_with_stdio(false);
    fin.tie(nullptr);
    
    fin>>n>>k;
    
    vector<long long int> v(n+1);
    
    for(i=1;i<=n;++i){
        fin>>v[i];
    }
    
    for(i=k;i<=n;++i){
        minn = LLONG_MAX;
        
        /*while(!dq.empty() && dq.front() > i - k){
            dq.pop_front();
        }*/
        
        
        inceput = i-k+1;
        while(inceput <= i){
            minn = min(minn, v[inceput]);
            inceput++;
        }
        
        
        //dq.push_back(i-k);
        
        
        suma += minn;
        
    }
    
    fout<<suma;
    
    
    
    return 0;
}