// verifast_options{disable_overflow_check target:ILP32}

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


extern void __assert_fail (const char *__assertion, const char *__file,
      unsigned int __line, const char *__function)
     __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__noreturn__));
extern void __assert_perror_fail (int __errnum, const char *__file,
      unsigned int __line, const char *__function)
     __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__noreturn__));
extern void __assert (const char *__assertion, const char *__file, int __line)
     __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__noreturn__));

void reach_error() //@ requires false; 
//@ ensures true;
{ ((void) sizeof ((0) ? 1 : 0), __extension__ ({ if (0) ; else __assert_fail ("0", "assert.h", 3, __extension__ __PRETTY_FUNCTION__); })); }
extern void abort(void);
void assume_abort_if_not(int cond) //@ requires true; 
//@ ensures true;
{
  if(!cond) {abort();}
}
void __VERIFIER_assert(int cond) //@ requires (1 <= cond); 
//@ ensures (1 <= cond);
{
  if (!(cond)) {
  ERROR: {reach_error();abort();}
  }
  return;
}
int __VERIFIER_nondet_int();//@ requires true; 
//@ ensures true;

int main() //@ requires module(gauss_sum__verifast_instrumented_modified, true); 
//@ ensures junk();
{
    int n, sum, i;
    n = __VERIFIER_nondet_int();
    if (!(1 <= n && n <= 1000)) return 0;
    sum = 0;
    for(i = 1; i <= n; i++)//@ invariant (((i + (sum * 2)) == (i * i)) && (((n + (n * n)) == (sum * 2)) || (i < (n + 1))));
 {
        sum = sum + i;
    }
    __VERIFIER_assert(2*sum == n*(n+1));
    return 0;
}