bool check(vector<int> &A, int B, int k)
{
    int cnt=0,sum=0;
    for(int i=0;i<A.size();i++)
    {   if(A[i]>k) return 0;
        if(sum+A[i]<=k)
        {
            sum+=A[i];
        }
        else
        {
            sum=A[i];
            cnt++;
        }
    }
    return cnt<B;
}
int Solution::books(vector<int> &A, int B) {
    if(A.size()<B) return -1;
    int low=0,high=INT_MAX,ans=-1;
    while(low<=high)
    {
        int mid=low+(high-low)/2;
        if(check(A,B,mid))
        {
            ans=mid;
            high=mid-1;
        }
        else
        {
            low=mid+1;
        }
    }
    return ans;
}