void abort() { };
                                                                                                                                                          
                                                                             

/*
 * Recursive computation of fibonacci numbers.
 * 
 * Author: Matthias Heizmann
 * Date: 2013-07-13
 * 
 */

extern int __VERIFIER_nondet_int();


/*@ 
    requires (1);
    ensures (((\result == 0) || (0 < n)));
@*/
int fibonacci(int n) {
    if (n < 1) {
        return 0;
    } else if (n == 1) {
        return 1;
    } else {
        return fibonacci(n-1) + fibonacci(n-2);
    }
}


int main() {
    int x = 9;
    int result = fibonacci(x);
    if (result == 34) {
        return 0;
    } else {
        ERROR: {/*@ assert(0); */;abort();}
    }
}