// verifast_options{disable_overflow_check target:ILP32}

extern void abort(void);//@ requires true; 
//@ ensures true;

extern void __assert_fail(const char *, const char *, unsigned int, const char *) __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__noreturn__));
void reach_error() //@ requires false; 
//@ ensures true;
{ __assert_fail("0", "Fibonacci01-1.c", 3, "reach_error"); }

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

extern int __VERIFIER_nondet_int(void);//@ requires true; 
//@ ensures true;



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


int main() //@ requires module(Fibonacci01_1__verifast_instrumented_modified, true); 
//@ ensures junk();
{
    int x = __VERIFIER_nondet_int();
    if (x > 46 || x == -2147483648) {
        return 0;
    }
    int result = fibonacci(x);
    if (result >= x - 1) {
        return 0;
    } else {
        ERROR: {reach_error();abort();}
    }
}