#include <bits/stdc++.h>
#define pb push_back

using namespace std;

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

void debug_out() { cerr << '\n'; }
template <typename Head, typename... Tail> void debug_out(Head H, Tail... T) { cerr << " " << H; debug_out(T...);}
#define dbg(...) cerr << #__VA_ARGS__ << " ->", debug_out(__VA_ARGS__)
#define dbg_v(x, n) do{cerr<<#x"[]: ";for(int _=0;_<n;++_)cerr<<x[_]<<" ";cerr<<'\n';}while(0)
#define dbg_ok cerr<<"OK!\n"

typedef pair<int,int> pii;
typedef long long int ll;
typedef long double ld;

const int DMAX = 1e5+10;

deque <pii> deq;

int n,k;
ll ans;

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(0);

    int t,i,j;
    int x,y,z;

    fin>>n>>k;

    for(i=1;i<=k;i++){
        fin>>x;
        while(!deq.empty() && deq.back().first >= x)
            deq.pop_back();
        deq.push_back({x,i});
    }
    ans+=deq.front().first;
    for(i=k+1;i<=n;i++){
        fin>>x;
        if(deq.front().second <= i-k)
            deq.pop_front();
        while(!deq.empty() && deq.back().first >= x)
            deq.pop_back();
        deq.push_back({x,i});
        ans+=deq.front().first;
    }
    fout<<ans<<'\n';

    return 0;
}