#include <iostream>
#include <fstream>
#include <deque>

using namespace std;

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

deque <pair<int,int>> q;
///         x   poz

int n,x,k,i;
long long sum;

int main()
{
    fin>>n>>k;
    for(i=1;i<=n;i++){
        fin>>x;
        while(!q.empty() && i-q.front().second+1>k)
            q.pop_front();
        while(!q.empty() && q.back().first>x)
            q.pop_back();
        q.push_back({x,i});
        if(i>=k)
            sum+=q.front().first;
    }
    fout<<sum<<'\n';
    return 0;
}