void abort() { };
                                 
  
                        
                                                                                                                                                          
                                                                            
extern int __VERIFIER_nondet_int();
                        
/*@ 
    requires (1);
    ensures ((cond != 0));
@*/
void assume_abort_if_not(int cond) {
  if(!cond) {abort();}
}
/*@ 
    requires ((1 <= cond)) && (cond != 0);
    ensures ((1 <= cond)) && (1);
@*/
void __VERIFIER_assert(int cond) {
    if (!(cond)) {
    ERROR:
        {/*@ assert(0); */;}
    }
    return;
}

int main() {
    int a, b;
    long long x, y, z;

    a = __VERIFIER_nondet_int();
    assume_abort_if_not(a>=0 && a<=1);
    b = __VERIFIER_nondet_int();
    assume_abort_if_not(b>=0 && b<=1);
    assume_abort_if_not(b >= 1);

    x = a;
    y = b;
    z = 0;

/*@
loop invariant ((((((z == 0) && (b == 1)) && (y == 1)) && (a == x)) || (((b == 1) && (a == z)) && (y == 0))));
@*/
    while (1) {
        __VERIFIER_assert(z + x * y == (long long) a * b);
        if (!(y != 0))
            break;

        if (y % 2 == 1) {
            z = z + x;
            y = y - 1;
        }
        x = 2 * x;
        y = y / 2;
    }
    __VERIFIER_assert(z == (long long) a * b);
    
    return 0;
}