#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define OPFI(x) freopen(#x".in", "r", stdin);\
                freopen(#x".out", "w", stdout)
#define REP(i, a, b) for(int i=(a); i<=(b); ++i)
#define REPd(i, a, b) for(int i=(a); i>=(b); --i)
inline ll rd(){
    ll r=0, k=1; char c; while(!isdigit(c=getchar())) if(c=='-') k=-k;
    while(isdigit(c)) r=r*10+c-'0', c=getchar(); return r*k;
}
ll n, m, ans;
int main(){
    n=rd(), m=rd();
    ans=min(n/3, m/3);
    n-=ans*3;
    m-=ans*3;
    if(n+m<=ans){
        printf("%lld\n", 2*ans-1);
    }else{
        if(n>m) swap(n, m);
        if(m<=ans){
            printf("%lld\n", 2*ans+1);
        }else{
            m-=ans;
            printf("%lld\n", 2*(ans+(m+3)/4)-1);
        }
    }
    return 0;
}