/*
ID: teparuf1
TASK: dualpal
LANG: C++
*/
#include <bits/stdc++.h>

#define MOD 1000000007
typedef long long int ll;
using namespace std;

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

int a[5000001];


int main()
{
    int n,k;
    fin >> n >> k;
    for(int i=1;i<=n;i++)fin >> a[i];
    ll res=0;
    deque<ll> Q;
    for(int i=1;i<=k;i++)
    {
        while(!Q.empty() && a[Q.back()]>a[i])Q.pop_back();
        Q.push_back(i);
    }
    res += a[Q.front()];
    for(int i=k+1;i<=n;i++)
    {
        while(!Q.empty() && a[Q.back()]>a[i])Q.pop_back();
        Q.push_back(i);
        while(!Q.empty() && Q.front() < i-k+1)Q.pop_front();
        res = res + a[Q.front()];
    }
    fout << res;

}