Công thức tính tổng dãy số Fibonacci

#include

using namespace std;

const int base = 1000000000;

const int base_digits = 9;

struct bigint

{

    vector a;

    int sign;

    bigint[] : sign[1]

    {

    }

    bigint[long long v]

    {

        *this = v;

    }

    bigint[const string &s]

    {

        read[s];

    }

    void operator=[const bigint &v]

    {

        sign = v.sign;

        a = v.a;

    }

    void operator=[long long v]

    {

        sign = 1;

        if [v 0; v = v / base]

            a.push_back[v % base];

    }

    bigint operator+[const bigint &v] const

    {

        if [sign == v.sign]

        {

            bigint res = v;

            for [int i = 0, carry = 0; i = v.abs[]]

            {

                bigint res = *this;

                for [int i = 0, carry = 0; i