code for ROUND 1 APAC 2017 QUESTION 3 GIVING WRONG ANSWER ON LARGE SUBTASK

gistfile1.txt

#include <bits/stdc++.h>

#define long long long int
using namespace std;
#define Max 1e18
# define con 1000000007
#define mp make_pair
#define pb push_back

#define PI 3.14159265
long ci[102];double r;int m;
double answer()
{
    double rr=1.0;double ans=0;
    for(int i=m;i>=1;i--)
    {
        ans+=rr*((double)ci[i]);
        rr*=(1.0+r);
    }
    ans-=((double)ci[0])*rr;
    return ans;
}
int main()
{
     ios::sync_with_stdio(false);cin.tie(0);
    // cout<<((1e-18)*1e9)<<endl;
ifstream filename;
filename.open("input.txt", ios::in);
ofstream file2;
file2.open("output.txt",ios::out);
int t;filename>>t;int i=1;
while(t-->0)
{
    filename>>m;
   for(int i=0;i<=m;i++)filename>>ci[i];
   long l=0,b=2e18;double ans,ans1;
   r=1-(1e-18);double right=answer();r=-1+(1e-18);double left=answer();//cout<<setprecision(12)<<fixed<<left<<endl<<right<<endl;
   while(l<=b)
   {
       long mid1=(b+l)/2;double mid=mid1;
       mid-=Max;
       mid/=(double)Max;
        r=mid;
        ans=answer();
        //cout<<setprecision(12)<<fixed<<l<<" "<<mid1<<" "<<b<<endl;
        if((ans>0.0 && left<0.0) ||(ans<0.0 && left>0.0)){right=ans;b=mid1-1;ans1=mid;}else if((ans<0.0 && right>0.0) ||(ans>0.0 && right<0.0)){left=ans;l=mid1+1;ans1=mid;}   else{ans1=mid;break;}
   }

   file2<<"Case #"<<i<<": ";
    file2<<setprecision(12)<<fixed<<ans1<<endl;i++;ans=0;
   //if(i==169) cout<<v<<" "<<d<<" "<<ans;
}
filename.close();
file2.close();
return 0;
}