#include <iostream>
#include <fstream>
#include <vector>

using namespace std;
fstream fin("transport.in");
ofstream fout("transport.out");

int transport( int c, int k, const vector<int>& v ){
    int ct = 0, nt = 0;
    for( size_t idx = 0; idx < v.size(); ){
        if( v[idx] > c )
            return 1;
        if( ct + v[idx] == c ){
            if( nt == k ){
                if( (idx + 1) == (idx < v.size()) )
                    return 0;
            }
            nt++;
            ct = 0;
            idx++;
        }
        else if( ct + v[idx] > c ){
            nt++;
            ct = 0;
        }
        else {
            ct = ct + v[idx];
            idx++;
        }
        if( nt > k )
            return 1;
    }
    if( ( ct > 0 ) && ( nt == (k-1) ) )
        return 0;
    return -1;
}

int main()
{
    vector<int> v;
    int n = 0, k = 0, s = 0, maxx = 0;
    fin >> n >> k;
    for( int i = 0; i < n; i++ ){
        int aux;
        fin >> aux;
        v.push_back(aux);
        s = s + aux;
        if( aux > maxx)
            maxx = aux;
    }
    int stg = maxx , drp = s, mij = 0;
    bool notFound = true;
    while( ( stg <= drp ) && notFound ) {
        mij = (stg + drp) / 2;
        int t = transport( mij, k, v );
        if( t == 0 )
            notFound = false;
        else{
            if( t > 0 ){
                stg = mij+1;
            }
            else {
                drp = mij-1;
            }
        }
    }
    if( notFound )
        fout << -1;
    else
        fout << mij;
    return 0;
}