C++ :

#include <iostream>
#include <stdio.h>
#include <algorithm>
using namespace std;
int a,b,c,N,x,y;
int main()
{
//	freopen("9L.in","r",stdin);
//	freopen("9L.out","w",stdout);
	cin >>N;
	a=b=1;
	for (int i=1; i<N; i++)
	{
		c=a+b;
		a=b;
		b=c;
	}
	cout << a<<endl;
	return 0;
}