#include<stdio.h>
 
/* getMissingNo takes array and size of array as arguments*/
int getMissingNo(int a[], int n)
{
    int i;
    int x1 = a[0]; /* For xor of all the elements in array */
    int x2 = 1; /* For xor of all the elements from 1 to n+1 */
 
    for (i = 1; i< n; i++)
        x1 = x1^a[i];
 
    for ( i = 2; i <= n+1; i++)
        x2 = x2^i;         
 
    return (x1^x2);
}
 
/*program to test above function */
int main()
{
    int a[] = {1, 2, 4, 5, 6};
    int miss = getMissingNo(a, 5);
    printf("%d", miss);
    getchar();
}

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