Help me in solving CLB088 problem

help
,
1

My issue

Not able to solve this question though i have submitted on the value as 6

My code

#include <stdio.h>

int main(){
    int arr[]={1,2,3,4,5};
    
    int size=sizeof(arr) / sizeof(arr[0]);
    
    arr[size -1] =6;
    
    printf ("last element:%d\n", arr[size -1]);
    
    return 0;
    
}

Learning course: Data structures & Algorithms lab
Problem Link: https://www.codechef.com/learn/course/muj-aiml-dsa-c/MUJADSAC05/problems/CLB088