nếu không có số tự nhiên x thì mình sẽ trả về -1 nhé

code:

#include <iostream>
using namespace std;
int main() {
    freopen("equa.inp","r",stdin);
    freopen("equa.out","w",stdout);
    long long a,b,c;
    cin >> a >> b >> c;
    if (b%c==0) cout << 0;
    else {
        long long d = (b%c)/a;
        if (a*d!=b%c) cout << -1;
        else cout << d;
    }
}

#include <bits/stdc++.h>
#define SmileHappy  int main()
#define ll long long
#define str string
#define fir first
#define sec second
#define ld long double
#define pb push_back
#define MOD 100000009
#define freopen(name) if(fopen(name".INP","r")) {freopen (name".INP","r",stdin); freopen (name".OUT","w",stdout);}
#define ALL(x) (x).begin(),(x).end()
using namespace std;
SmileHappy
{

  freopen("EQUA");
  int a, b, p;
  cin >> a >> b >> p;
  int gcd = __gcd(a, p);
  if (gcd == 1) {
    int x;
    for (x = 0; x < p; x++)
    {
      if (a * x % p == b) break;
    }
    cout << x << endl;
  }
  else cout << -1 << endl;

  return 0;
}