Problem:
Score : 300 points

Problem Statement

Snuke loves puzzles.

Today, he is working on a puzzle using S- and c-shaped pieces.
In this puzzle, you can combine two c-shaped pieces into one S-shaped piece, as shown in the figure below:

Snuke decided to create as many Scc groups as possible by putting together one S-shaped piece and two c-shaped pieces.

Find the maximum number of Scc groups that can be created when Snuke has N S-shaped pieces and M c-shaped pieces.

Constraints

1 ≤ N,M ≤ 10^{12}

Input

The input is given from Standard Input in the following format:

N M

Output

Print the answer.

Sample Input 1

1 6

Sample Output 1

2

Two Scc groups can be created as follows:

Combine two c-shaped pieces into one S-shaped piece

Create two Scc groups, each from one S-shaped piece and two c-shaped pieces

Sample Input 2

12345 678901

Sample Output 2

175897

Solution in C (GCC 5.4.1) (judge verdict: Accepted)

#include <stdio.h>

typedef long long ll;


int main(){

	ll N,M;

	scanf("%lld %lld",&N,&M);

	ll l=0;
	ll r=1000000000000ll;

	ll ans=0ll;

	while(l<r){
		ll mid=(l+r)/2ll;
		if(mid-N<=(M-(2ll*mid))/2ll && M>=2ll*mid){
			l=mid+1;
			if(ans<mid){ans=mid;}
		}
		else{
			r=mid;
		}
	}
	printf("%lld\n",ans);

	return 0;
}