#include <bits/stdc++.h>
using namespace std;

#define int long long
//#define uint __int128_t

#define pb push_back
#define fi first
#define se second
#define rep(i,s,n) for(int i = s;i<n;i++)
#define repe(i,s,n) for(int i = s;i<=n;i++)
#define rrep(i,s,n) for(int i = (n)-1;i>=(s);i--)
#define all(v) (v).begin(),(v).end()
#define chmin(a,b) a=min((a),(b))
#define chmax(a,b) a=max((a),(b))
#define low(a,b) lower_bound(all(a),(b))-(a).begin()
#define upp(a,b) upper_bound(all(a),(b))-(a).begin()
#define endl '\n'
#define IOS() ios_base::sync_with_stdio(0);cin.tie(0)
typedef long long ll;
typedef pair<int,int>pint;
typedef vector<int>vint;
typedef vector<vint> vvint;
typedef vector<pint>vpint;
typedef pair<pint,int> P1;
typedef pair<int,pint> P2;
typedef pair<pint,pint> PP;
static const ll maxLL = (ll)1 << 62;
const ll MOD=1000000007;
const ll INF=1e18;

int A,B;

signed main() {
    IOS();
    //(1ll<<N)シフト演算のオーバーフローに気をつける
    //MOD同士の引き算に注意
    cin>>A>>B;
    int ans=0;
    rep(i,A,B+1){
        if((A+B+i)%3==0)ans++;
    }
    cout<<ans<<endl;
    
    
    
    
    
    
    
    
    
    
    
    
    
    return 0;
}