#include <stdio.h>
#include <math.h>
int add(int a, int b) {
while (b != 0) {
int sum = a & b;
a = a ^ b;
b = sum << 1;
}
return a;
}
int main(void) {
int a = -13;
int b = 42;
int sum = add(a, b);
printf("%d + %d = %d\n", a, b, sum);
return 0;
}