GATE Computer Science (CS) 2016 Shift 1 Solved Paper

Consider the following C program.
#include<stdio.h>
void mystery (int *ptra, int *ptrb) {
                int *temp;
                temp = ptrb;
                ptrb = ptra;
                ptra = temp;
}
int main () {
                int a=2016, b=0, c=4, d=42;
                mystery (&a, &b);
                if (a < c)
                mystery (&c, &a);
                mystery (&a, &d) ;
                print ("%d\n", a);
}
The output of the program is __________.