Wrong output in Merge Sort Algorithm

I've followed all the algorithm steps very carefully , but still this always outputs me the wrong answer. I don't understand why. I think something's wrong in the merge algorithm that's causing this but cannot pinpoint what. Please help. Also if there is anything that can be done to improve the code please suggest.

Thank you

INPUT - {5,6,1,8,9,7}

OUTPUT - {1,0,7,0,9,7}

#include<stdio.h>
#include<malloc.h>

void mergeSort(int array[],int length);
void merge(int *leftArray,int *rightArray,int *array);

void main()
{

    int array[] = {5,6,1,8,9,7};
    int length_of_array;

    length_of_array = sizeof(array) / sizeof(array[0]);

    mergeSort(array,length_of_array);

    int i;

    for(i=0;i<length_of_array;i++)
    {
        printf("%d->",array[i]);
    }
}

void mergeSort(int array[],int length)
{

    if(length <  2)
        return;


    int mid;
    int i;

    mid = length/2;

    int *leftArray, *rightArray;

    leftArray = (int*)malloc(mid*sizeof(int));
    rightArray = (int*)malloc((length-mid)*sizeof(int));

    for(i=0;i<mid;i++)
        leftArray[i] = array[i];

    for(i=mid;i<length;i++)
        rightArray[i-mid] = array[i];


    mergeSort(leftArray, mid);
    mergeSort(rightArray, length-mid);

    merge(leftArray,rightArray,array);

}

void merge(int *leftArray,int *rightArray,int *array)
{
    int i,j,k;
    i = j = k = 0;

    int leftSize = sizeof(leftArray)/sizeof(leftArray[0]);
    int rightSize = sizeof(rightArray)/sizeof(rightArray[0]);

    while(i < leftSize && j < rightSize)
    {
        if(leftArray[i]<rightArray[j])
        {
            array[k] = leftArray[i];
            k = k + 1;
            i = i + 1;
        }
        else
        {
            array[k] = rightArray[j];
            k = k + 1;
            j = j + 1;
        }

    }

    while(i<leftSize)
    {
        array[k] = leftArray[i];
        k = k + 1;
        i = i + 1;

    }

    while(j<rightSize)
    {
        array[k]  = rightArray[j];
        k = k + 1;
        j = j + 1;

    }

}