#include <iostream>
#include <math.h>

using namespace std;

float f(float x){
  return x*x-5*x-3;
}

float bisect(float lower, float upper, float (*func)(float)){
  float mid = (lower + upper) / 2;

  if((*func)(upper) == 0)
    return upper;
  else if((*func)(lower) == 0)
    return lower;
  else if((*func)(mid) == 0)
    return mid;

  if((func(mid) > 0 && func(upper) < 0) || (func(mid) < 0 && func(upper) > 0))
    return bisect(mid, upper, func);
  else
    return bisect(lower, mid, func);
}

int main(){
  float n1 = -10, n2 = 10, nst;

  nst = bisect(n1, n2, f);

  cout << nst << endl;

  return 0;
}