nfibonacchi.cpp

/*Problem statement
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The n-th term of Fibonacci series F(n), where F(n) is a function, is calculated using the following formula -

    F(n) = F(n - 1) + F(n - 2), 
    Where, F(1) = 1, F(2) = 1

Provided 'n' you have to find out the n-th Fibonacci Number. Handle edges cases like when 'n' = 1 or 'n' = 2 by using conditionals like if else and return what's expected.
"Indexing is start from 1"
Example :
Input: 6
Output: 8
Explanation: The number is ‘6’ so we have to find the “6th” Fibonacci number.
So by using the given formula of the Fibonacci series, we get the series:    
[ 1, 1, 2, 3, 5, 8, 13, 21]
So the “6th” element is “8” hence we get the output.
Detailed explanation ( Input/output format, Notes, Images )
Sample Input 1:
6
Sample Output 1:
8
Explanation of sample input 1 :
The number is ‘6’ so we have to find the “6th” Fibonacci number.
So by using the given formula of the Fibonacci series, we get the series:    
[ 1, 1, 2, 3, 5, 8, 13, 21]
So the “6th” element is “8” hence we get the output.
Expected time complexity :
The expected time complexity is O(n).
Constraints:
1 <= 'n' <= 10000     
Where ‘n’ represents the number for which we have to find its equivalent Fibonacci number.
Time Limit: 1 second
*/


#include<iostream>
using namespace std;
int main(){
    int n;
    cin>>n;
    int n1=1, n2=1 , n3;
    for(int i=3;i<=n;i++){
        n3=n1+n2;
        n1=n2;
        n2=n3;    
    }
    cout<<n2;  
  return 0;  
}