C :

#include<stdio.h>

int step(int n) {
    if (n == 1) {
        return 1;
    }
    if (n == 2) {
        return 2;
    }
    return step(n - 1) + step(n - 2);
}

int main() {
    int n;
    while(~scanf("%d", &n)) {
        printf("%d\n", step(n));
    }
    return 0;
}

C++ :

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

Pascal :

var i,j,n:integer;
    a:array[0..1000]of longint;
begin
  readln(n);
  a[1]:=1;
  a[2]:=2;
  for i:=3 to n do a[i]:=a[i-1]+a[i-2];
  write(a[n]);
end.

Python :

# coding=utf-8
n=int(input())
if n==1:
    s=1
if n==2:
    s=2
if n>=3:
    a=1
    b=2
    
    for i in range(3,n+1):
        c=a+b
        a=b
        b=c
    s=c
print(s)