#include <fstream>
#include <deque>
#define ll long long

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

std::deque<std::pair<int, int>>dq;

int main() {
	std::ios::sync_with_stdio(false);
	fin.tie(0);
	fout.tie(0);
	ll n, c, k, s = 0;
	fin>>n>>k;
	for(int i=0;i<n;i++) {
		fin>>c;
		while(!dq.empty() and dq.front().second<=i-k) dq.pop_front();
		while(!dq.empty() and dq.back().first>=c) dq.pop_back();
		dq.push_back({c, i});
		if(i>=k-1) s+=dq.front().first;
	}
	fout<<s;
}