text: #include<iostream>
  using namespace std;
  
  int binaryStrings(int n){
      if(n==0) return 0;
     if(n==1) return 2;
     if(n==2) return 3;
     return binaryStrings(n-1) + binaryStrings(n-2);
      
  }
  int main(){
  	int n;
  	cin>>n;
  	cout<<"Numbers without consecutive 1's are - "<<binaryStrings(n)<<endl;
  	return 0;
  	
  }
  