C :

#include <stdio.h>
int main(void)
{
	int N;
	int n1 = 1,n2 =2,n3,i;
	while(scanf("%d",&N) != EOF)
	{
		if(N == 1)
		{
			printf("%d\n",n1);
		}
		else if(N == 2)
		{
			printf("%d\n",n2);
		}
		else
		{
			n1 = 1;
			n2 = 2;
			for(i=3;i<=N;i++)
			{
				n3 = n1 + n2;
				n1 = n2;
				n2 = n3;
			}
			printf("%d\n",n3);
		}
	}
	return 0;
}

C++ :

#include <stdio.h>
int main()
{
	int n;
	int a[]={1,1,2,3,5,8,13,21,34,55,89,144,233,377,610,987,1597,2584,4181,6765,10946};
	scanf("%d",&n);
	while(n!=0)
	{
		printf("%d\n",a[n]);
		n=0;
		scanf("%d",&n);
	}
	return 0;
}

Pascal :

var i,n:longint;
    a,b,c:qword;
begin
  while not eof do
  begin
  readln(n);
    a:=1;b:=2;
    for i:=3 to n do
      begin
        c:=a+b;
        a:=b;
        b:=c;
      end;
   if n=1 then writeln(1);
   if n=2 then writeln(2);
   if n>=3 then writeln(c);
  end;
end.

Java :

import java.io.PrintStream;
import java.util.Scanner;

public class Main {
	static int  add(int n)
	{
	if(n==1||n==2) return n;
	else return add(n-1)+add(n-2);
	}
	public static void main(String[] args )
	{
	int n,sum;
	Scanner sc = new Scanner(System.in);
	 PrintStream ps = new PrintStream(System.out);
	while(sc.hasNext())
	{ n= sc.nextInt();
	  sum=add(n);
	 ps.printf("%d\n",sum);
	}
		
	}
}