P3743 怎么总是输出0啊，路过dalao帮帮忙。感谢

#include<bits/stdc++.h>
using namespace std;
#define int long long
inline int read()
{
    int x=0,f=1;
    char ch=getchar();
    while(ch<'0'||ch>'9')
    {
        if(ch=='-')
            f=-1;
        ch=getchar();
    }
    while(ch>='0' && ch<='9')
        x=x*10+ch-'0',ch=getchar();
    return x*f;
}
void write(int x)
{
    if(x<0)
        putchar('-'),x=-x;
    if(x>9)
        write(x/10);
    putchar(x%10+'0');
    return;
}
const int maxN = 1E5+10;
const double minN = 1E-6;
int N;
double P,a[maxN],b[maxN];
bool ch(double n){
	double s = 0;
	for(int i = 0; i < N; ++ i)s += (a[i]*n > b[i])*(a[i]*n-b[i]);
	return s<=P*n;
}
double s,t,m;
signed main(){
	N = read();
	for(int i = 0; i < N; ++ i){
		cin>>a[i]>>b[i];
		s += a[i];
	}
	if(s <= P){
		cout<<-1; return 0;
	}
	s = 0;
	while(t-s > minN){
		m = (t+s)/2;
		if(ch(m))s = m;
		else t = m;
	}
	cout<<fixed<<setprecision(10)<<s;
	return 0;
}