#include <iostream>
long int fibonacci(const int );
int main()
    {
    int N;
    std:: cin>>N;
    const int M=N;
    std::cout << fibonacci(M)*2;;
    return 0;
    }
long int fibonacci(const int n)
     {   const int m = n;
         long int t[m],i;
         int first = 0, second = 1;
         t[first]=0; t[second]=1;
         for (i=second+1; i<m-1; ++i)
         {
             t[i] = t[first] + t[second];
             first = second;
             second = i;
         }

        return t[i];
     }

Edited by author 10.05.2010 18:58

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