Question: walk the grid

Problem Description
There are n grids numbered 1-n. The robot walks backwards from grid 1 to grid n, and needs to go out from grid n. The robot has an initial energy, and each grid corresponds to an integer A[i], which represents the energy value of this grid. If A[i] > 0, the robot can get A[i] energy by walking to this grid. If A[i] < 0, it needs to consume the corresponding energy when walking to this grid. If the robot's energy is < 0, it cannot continue. Go ahead. Ask how much initial energy the robot needs to have to complete the entire journey.

For example: n = 5. {1, -2, -1, 3, 4} requires at least 2 initial energies to go from square 1 to square 5. The energy change on the way is as follows 3 1 0 3 7.
Input
Line 1: 1 number n, representing the number of grids. (1 <= n <= 50000)
Line 2 - n + 1: 1 number A[i] in each line, representing the energy value in the grid (-1000000000 <= A[i] <= 1000000000)
Output
Output 1 number, corresponding to the minimum initial energy required to go from 1 to n.
Sample Input
5
1
-2
-1
3
4
Sample Output
2

AC code

#include <iostream>

using namespace std;

int main()
{
    int n;
    cin>>n;
    int a[n];
    for(int i=0;i<n;i++){
        cin>>a[i];
    }
    int minenergy=0,sum=0;
    for(int i=0;i<n;i++){
        sum+=a[i];
        if(sum<minenergy){
            minenergy=sum;
        }
    }
    cout<<-minenergy;
    return 0;
}