#include<bits/stdc++.h>
using namespace std;

string numeFisier="deque";
ifstream fin(numeFisier+".in"); ofstream fout(numeFisier+".out");
#define cin fin
#define cout fout

#define INIT  ios_base :: sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
#define mp make_pair
#define pb push_back
#define ft first
#define sc second
#define ll long long
#define pii pair<int, int>
#define count_bits __builtin_popcount
#define int ll


int t, n, m, k, a[5000010], q, l, r;



int32_t main(){
INIT
cin>>n>>k;
for(int i=1; i<=n; i++){
    cin>>a[i];
}

int sum=0;
int beg=1, en=k;
deque<int32_t> dq;

for(int i=1; i<=k; i++){
    while((!dq.empty()) && (a[(int32_t)dq.back()]>=a[i]) ){
        dq.pop_back();
    }
    dq.push_back(i);
}

sum+=a[(int32_t)dq.front()];

for(beg++, en++;en<=n;beg++, en++){
    while((!dq.empty()) && beg>dq.front()){
        dq.pop_front();
    }
    while((!dq.empty()) && (a[(int32_t)dq.back()]>=a[en])){
        dq.pop_back();
    }
    dq.push_back(en);
    sum+=a[(int32_t)dq.front() ];
}
cout<<sum;

return 0;
}