Help me in solving FOURARR problem

help
,
1

My issue

Is there any alternate approach rather than using fft, here?

My code

#include <bits/stdc++.h>
using namespace std;

int main() {
	int a, b, c, d, k;
	cin>>a>>b>>c>>d>>k;
	
	int arr[a], brr[b], crr[c], drr[d];
	
	for(int i=0; i<a; i++){
	    cin>>arr[i];
	}
	
	for(int i=0; i<b; i++){
	    cin>>brr[i];
	}
	
	for(int i=0; i<c; i++){
	    cin>>crr[i];
	}
	
	for(int i=0; i<d; i++){
	    cin>>drr[i];
	}
	vector<int> err, frr, grr;
	
	for(int i=0; i<a; i++){
	    for(int j=0; j<b; j++){
	        err.push_back(arr[i]+brr[j]);
	    }
	}
	
	for(int i=0; i<c; i++){
	    for(int j=0; j<d; j++){
	        frr.push_back(crr[i]+drr[j]);
	    }
	}
	
	for(int i=0; i<a*b; i++){
	    for(int j=0; j<c*d; j++){
	        grr.push_back(err[i]*frr[j]);
	    }
	}
	
	sort(grr.begin(), grr.end());
	
	cout<<grr[k]<<endl;
	
	
}

Problem Link: Four Arrays Practice Coding Problem - CodeChef