#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define double long double;
#define pb push_back
#define endl '\n'
#define fs first
#define sc second
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
#define mod 1000000007
#define INF LONG_LONG_MAX

int k, a[5000015], d[5000015], n;

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

void solve()
{
    fin>>n>>k;
    for(int i=1;i<=n;i++)
        fin>>a[i];
    ll ans=0;
    int f=1, b=0;
    for(int i=1;i<=n;i++)
    {
        while(f<=b && a[i]<=a[d[b]])
        {
            b--;
        }
        d[++b]=i;
        if(i-d[f]==k){f++;}
        if(i>=k){ans+=a[d[f]];}
    }
    fout<<ans;
}

int32_t main()
{
    ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
    ll tc=1;
    //cin>>tc;
    while(tc--)
    {
        solve();
    }
    return 0;
}