#include <bits/stdc++.h>
using namespace std;
int v[5000005], minn[5000005];
int main()
{
    ifstream cin("deque.in");
    ofstream cout("deque.out");
    deque<int> dq;
    long long int n, k, sum=0;
    cin>>n>>k;
    for(int i=0; i<n; i++)
    {
        cin>>v[i];
    }
    for(int i=0; i<k; i++)
    {
        while(!dq.empty() && v[dq.back()]>v[i])
            dq.pop_back();
        dq.push_back(i);
    }
    minn[0]=v[dq.front()];
    for(int i=k; i<n; i++)
    {
        if(dq.front()<=i-k)
            dq.pop_front();
        while(!dq.empty() && v[dq.back()]>v[i])
            dq.pop_back();
        dq.push_back(i);
        minn[i-k+1]=v[dq.front()];
    }
    for(int i=0; i<n-k+1; i++)
        sum+=minn[i];
    cout<<sum;
    return 0;
}