为什么我的代码结果完全不对？？？

#include <bits/stdc++.h>
#include <cmath>
using namespace std;
int main () {
    float a, b, c, p, s;
    cin >> a >> b >> c;
    p = (a + b + c) * 2;
    s = sqrt (p * (p - a) * (p - b) * (p - c));
    cout << s;
}```