Problem D in educational codeforces round 66

Problem : https://codeforces.com/contest/1175/problem/D

my solution :

#include
#include
#include
#include
using namespace std;

int main()
{
long long int n,k,i,j,a,b,sum=0,d,f=0;

	cin>>n>>k;
	
	vector <long long int> v(n);
	
	for(i=0;i<n;i++)
		cin>>v[i];
		
	a=n-1;	
	
	for(i=k;i>0;i--)
	{
		sum=0;
		d=LONG_MIN;
		if(i!=1)
		{
			for(j=a;j>=(i-1);j--)
			{	
				sum+=v[j];
				if(sum>d)
				{
					d=sum;
					a=j;
					a--;
				}
			}
			f+=(d*i);
			//cout<<"f="<<f<<" d="<<d<<" i="<<i<<endl;
		}
		else
		{
			sum=0;
			for(j=0;j<=a;j++)
				sum+=v[j];
			f+=sum;
		//cout<<f<<endl;
		}
	}
	cout<<f<<endl;

}

I am getting wrong answer on pretest 6.