#include<bits/stdc++.h>
using namespace std;
#define ALL(x) x.begin(),x.end()
#define rep(i,n) for(int i=0;i<(n);i++)
#define debug(v) cout<<#v<<":";for(auto x:v){cout<<x<<' ';}cout<<endl;
#define mod 1000000007
using ll=long long;
const int INF=1000000000;
const ll LINF=1001002003004005006ll;
int dx[]={1,0,-1,0},dy[]={0,1,0,-1};
// ll gcd(ll a,ll b){return b?gcd(b,a%b):a;}
template<class T>bool chmax(T &a,const T &b){if(a<b){a=b;return true;}return false;}
template<class T>bool chmin(T &a,const T &b){if(b<a){a=b;return true;}return false;}

struct IOSetup{
    IOSetup(){
        cin.tie(0);
        ios::sync_with_stdio(0);
        cout<<fixed<<setprecision(12);
    }
} iosetup;
 
template<typename T1,typename T2>
ostream &operator<<(ostream &os,const pair<T1,T2>&p){
    os<<p.first<<" "<<p.second;
    return os;
}
 
template<typename T>
ostream &operator<<(ostream &os,const vector<T>&v){
    for(int i=0;i<(int)v.size();i++) os<<v[i]<<(i+1==(int)v.size()?"":" ");
    return os;
}

template<typename T1,typename T2>
istream &operator>>(istream &is,pair<T1,T2>&p){
    is>>p.first>>p.second;
    return is;
}

template<typename T>
istream &operator>>(istream &is,vector<T>&v){
    for(T &x:v)is>>x;
    return is;
}


signed main(){
    int n,k;cin>>n>>k;
    vector<ll> a(n);
    cin>>a;

    vector<ll> sum(1,0);
    rep(i,n)sum.push_back(sum.back()+a[i]);
    rep(i,n)sum.push_back(sum.back()+a[i]);
    ll db[n][21];
    rep(i,n) db[i][0]=a[i];

    rep(j,20){
        rep(i,n){
            db[i][j+1]=db[i][j]+db[(i+(1<<j))%n][j];
        }
    }

    auto check=[&](ll m){
        if(sum[n]<m*k) return false;

        ll d[n][21];
        rep(i,n){
            // 何個使うか
            int lw=1,hi=n,res=1;
            while(lw<=hi){
                int mid=(lw+hi)/2;
                if(sum[i+mid]-sum[i]>=m){
                    res=mid;
                    hi=mid-1;
                }else{
                    lw=mid+1;
                }
            }
            d[i][0]=res;
        }

        rep(j,20){
            rep(i,n){
                int nxt=(i+d[i][j])%n;
                d[i][j+1]=d[i][j]+d[nxt][j];
            }
        }
        
        ll mi=LINF,mindex=-1;
        rep(i,n){
            ll cnt=0;int p=i;
            for(int j=0;j<20;j++){
                if((k>>j)&1){
                    cnt+=d[p][j];
                    p=(p+d[p][j])%n;
                }
            }
            if(chmin(mi,cnt))mindex=i;
        }
        return mi<=n;
    };


    ll lw=1,hi=100000050000000,res=-1;
    while(lw<=hi){
        ll mid=(lw+hi)/2;
        if(check(mid)){
            res=mid;
            lw=mid+1;
        }else{
            hi=mid-1;
        }
    }
    cout<<res<<endl;
    return 0;
}