#include <bits/stdc++.h>
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
deque<pair<int,int>> q;
int n,k,i,x;
long long s;
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    in>>n>>k;
    while(n--)
    {
        ++i;
        in>>x;
        while(!q.empty() && q.front().second<=i-k)
            q.pop_front();
        while(!q.empty() && q.back().first>x)
            q.pop_back();
        q.push_back({x,i});
        if(i>=k)
            s+=q.front().first;
    }
    out<<s;
}