#pragma comment(linker, "/stack:200000000")
#pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#define _CRT_SECURE_NO_WARNINGS
#include <bits/stdc++.h>
using namespace std;
#define x first
#define y second
#define dbg(x) cout << #x << '=' << x << '\n';
#define ll long long
#define pi pair<int,int>
#define pl pair<ll,ll>
#define pd pair<double,double>
#define ld long double
#define pld pair<ld,ld>
#define lg length()
#define sz size()
#define pb push_back
#define MAXN 100005
#define INF 1000000005
#define LINF 1000000000000000005
#define x1 xdddddddddddddddddd
#define y1 ydddddddddddddddddd

ll n,k,s,x;

deque <pl> q;

int32_t main(){
    ios_base :: sync_with_stdio(0); cin.tie(); cout.tie();
    ifstream cin("deque.in");
    ofstream cout("deque.out");
    cin >> n >> k;
    for(int i=1;i<=n;i++){
        cin >> x;
        while(q.sz && x<=q[q.sz-1].x) q.pop_back();
        q.push_back({x,i});
        if(i>=k){
            s+=q[0].x;
            if(q[0].y==i-k+1) q.pop_front();
        }
    }
    cout << s;

}