C :

#include<stdio.h>
int getTotalCount(int monthCount)
    {
        int count ;
        if(monthCount>=4){
            count = getTotalCount(monthCount-1)+getTotalCount(monthCount-2);
        }else if(monthCount==3){
            count = 2;
        }else {
            count =1;
        }
        return count;
    }
    
int main()
{
	int n;
	scanf("%d",&n);
	printf("%d",getTotalCount(n));
 } 
    
  

C++ :

#include <iostream>
#include <cmath>
using namespace std;

//求第n个月兔子的总数量，a(n) = a(n-1) + a(n-2) 
int tuzi(int n){
	int r = 0;
	//交代起始项
	if(n == 1 || n == 2){
		r = 1;
	} else{
		r = tuzi(n - 1) + tuzi(n - 2); 	
	}
	
	return r;
}

int main(){
	int n,i;
	cin>>n;
	cout<<tuzi(n);
}

Python :

def f(num):
    if num<1:
        return -1
    elif num==1 or num==2 :
        return 1
    else :
        return f(num-1)+f(num-2)
a=int(input())
r=f(a)
if a!= -1:
    print(r)