Find the specific cubic root that solves the constraint using binary search

I am trying to find a cubic root(t) for the following equation, constraints

F(t)=A(t^3)+B(t^2)+C*(t)+D, F(t)<=10^18.
Help find t such that F(t+1) > K, and F(t) <= K

I have tried the following approach;

What I did is followed binary search approach.Intially put t value as k/2 in the equation. If the result value is greater than k, I will try with t value k/4.Else if result less than k, I will check wit t value k/4. The program seems works with smaller values of k but the problem is the values exceeding the range for larger k. I guess I should pickup a better pivot value(intiall value) or change some equation

    int a,b,c,d;
    long long int k,x,y;
    long long int i,f,temp1;
    int def;

    def=0;
    cin>>a>>b>>c>>d>>k;
    i=1;
    f=k;
    temp1=(1+k)/2;
    while((temp1>=1)&&(temp1<=k))
    {
        x=a*(temp1+1)*(temp1+1)*(temp1+1)+b*(temp1+1)*(temp1+1)+c*(temp1+1)+d;
        y=a*(temp1)*(temp1)*(temp1)+b*temp1*temp1+c*temp1+d;
        if((x>k)&&(y<=k))
        {
            cout<<temp1<<endl;
            def=1;
            break;
    }
    else if(x<k)
    {
        i=temp1;
        temp1=(f+temp1)/2;

    }
    else if(x>k)
    {
        f=temp1;
        temp1=(i+temp1)/2;
    }

}
        if(def==0)
         cout<<def<<endl;
       return 0;
}