could not able to figure out problem of fibonacii question? [on hold]

i had some how but cant figure out the problemto solve this problem of fibonacci sequence.Fibonnaci numbers commonly denoted Fn form a sequence, called the Fibonacci sequence, such that each number is the sum of the two preceding ones, starting from 0 and 1. what i did im doing im checking range between number after that what to do?

      F0 = 0 
      F1 = 1 
      Fn = Fn − 1 + Fn − 2, for integer n > 1.
    One way of generalizing the Fibonacci sequence is by starting with any pair of numbers and extending to negative values of n.
    Given two terms of a generalized Fibonacci sequence a and b, their positions c and d respectively and a position e, find res.

           input 
            0 1
            6 13
            10
           output 
            89
           input
            3 65
            6 315
            -10
           output
            4620
           input
            9 36
            15 646
            -5
            output
            -1/4      








      void solve(int N, int K) 
                { 
                    vector<long long int> Array(N + 1, 0); 

                    // If N is less than K 
                    // then the element is '1' 
                    if (N <= K) { 
                        cout << "1" << endl; 
                        return; 
                    } 

                    long long int i = 0, sum = K; 

                    // first k elements are 1 
                    for (i = 1; i <= K; ++i) { 
                        Array[i] = 1; 
                    } 

                    // (K+1)th element is K 
                    Array[i] = sum; 

                    // find the elements of the 
                    // K-Fibonacci series 
                    for (int i = K + 2; i <= N; ++i) { 

                        // subtract the element at index i-k-1 
                        // and add the element at index i-i 
                        // from the sum (sum contains the sum 
                        // of previous 'K' elements ) 
                        Array[i] = sum - Array[i - K - 1] + Array[i - 1]; 

                        // set the new sum 
                        sum = Array[i]; 
                    } 
                    cout << Array[N] << endl; 
                } 

                // Driver code 
                int main() 
                { 
                    long long int N = 4, K = 2; 

                    // get the Nth value 
                    // of K-Fibonacci series 
                    solve(N, K); 

                    return 0; 
                }