#include <bits/stdc++.h>

std::ifstream f("deque.in");
std::ofstream g("deque.out");

int n, k, A[5000002]; long long s;
int main(){
    std::deque<int> dq;
    f>>n>>k;
    for(int i=1, x; i<=n; ++i){
        f>>A[i]; 
        while(!dq.empty() and A[i] <= A[dq.back()]) 
            dq.pop_back();
        dq.push_back(i); 
        if(dq.front() == i-k) dq.pop_front();
        if(i>=k) s+=A[dq.front()];
    }
    g<<s<<'\n';
    return 0;
}