#include <iostream>
#include <fstream>
#include <deque>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
struct z{
    long long val, poz;
};
deque <z> v;
int main() {
    long long n,k,x;
    long long s=0;
    f>>n>>k;
    for(int i=1;i<=n;i++)
    {
        f>>x;
        while(!v.empty()&&v.back().val>x)
            v.pop_back();
        v.push_back({x,i});
        while(!v.empty()&&v.front().poz==i-k)
            v.pop_front();
        if(i>=k&&n>=i)
            s+=v.front().val;
    }
    cout<<s<<endl;
    return 0;
}