#include <iostream>
#include <vector>
#include <algorithm>
#include <utility>
#include <iterator>
#include <functional>
#include <bitset>
#include <string>

using namespace std;

long long n,k;
vector<long long>v;
vector<long long>dp(n+1000,1000000000);
vector<long long>price;


auto main()->int
{
    cin>>n>>k;
    price.push_back(0);
    for(auto i=1;i<=n;i++)
    {
        long long c;
        cin>>c;
        price.push_back(price[i-1] + c);
    }
    long long minie = 1000000000;
    for(auto i=1;i<=n;i++)
    {
        if(i-k+(n-i)==n-1)
        {
            minie = min(minie, price[i]);
        }
    }
    cout<<minie;
}