C :

#include<stdio.h>
int main()
{   
    int i,n,a[31];
    while(scanf("%d",&n)!=EOF)
	{ 
		a[0]=0;
		a[1]=1;
		for(i=2;i<=n;i++)
			a[i]=a[i-1]+a[i-2];
		printf("%d\n",a[n]);
	}   
  return 0;
}

C++ :

#include <stdio.h>

int Fibonacci(int n){
	if(n==0){
		return 0;
	}else if(n <= 2){
		return 1;
	}else{
		return Fibonacci(n-1) + Fibonacci(n-2);
	}
}

int main(){
    int f[33] = {0, 1, 1};
    for(int i=3; i<=30; i++){
        f[i] = f[i-1] + f[i-2];
    }
    int n;
    while(scanf("%d", &n) != EOF){
        printf("%d\n", f[n]);
    }

    return 0;
}

Pascal :

var i,n:longint;
    a,b,c:qword;
begin
  while not eof do
  begin
  readln(n);
    a:=0;b:=1;
    for i:=2 to n do
      begin
        c:=a+b;
        a:=b;
        b:=c;
      end;
   if n=0 then writeln(0);
   if n=1 then writeln(1);
   if n>=2 then writeln(c);
  end;
end.

Python :

while True:
    n=int(input())
    a1 = 1  
    a2 = 1 
    an = 0
    if(n>2):
        for i in range(1,n-1):
            an=a1+a2
            a1=a2
            a2=an
    elif(n>0):
        an=1
    else:
        an=0
    print(an)