C :

#include <stdio.h>
#include <stdlib.h>

int main()
{
    int n,i;
    scanf("%d",&n);
   long long  fib[55];
   fib[1]=1;fib[2]=1;
   for(i=3;i<=n;i++)
   {
       fib[i]=fib[i-1]+fib[i-2];
   }
    printf("%lld\n",fib[n]);
    return 0;
}

C++ :

#include<iostream>;
using namespace std;
int n,a,b,c,d;
int main()
{
   cin>>n;
   if(n<=2) cout<<"1";
   else
   {
    a=1;b=1;
    for(d=2;d<=n-1;d++)
    {c=a+b;a=b;b=c;}
    cout<<c;
   }
    return 0;
}

Pascal :

var i,j,n:integer;
    a:array[0..1000]of longint;
begin
  readln(n);
  a[0]:=0; a[1]:=1;
  for i:=2 to n do a[i]:=a[i-1]+a[i-2];
  writeln(a[n]); 
end.