I'm getting error while running this on leetcode

Question: Given an array nums. We define a running sum of an array as runningSum[i] = sum(nums[0]…nums[i]).

Return the running sum of nums.

Code:

class Solution {
public int[] runningSum(int[] nums) {
    int[] ans = new int[nums.length];
    
for(int i = 0; i < nums.length; i++) {
        ans[i] = nums[i] + nums[i+1];
    }
    return ans;
}

}

error:
java.lang.ArrayIndexOutOfBoundsException: Index 4 out of bounds for length 4
at line 6, Solution.runningSum
at line 54, __DriverSolution__.__helper__
at line 84, __Driver__.main