import std.stdio, std.string, std.conv;
import std.range, std.algorithm, std.array, std.typecons, std.container;
import std.math, std.numeric, core.bitop;


void main() {
    int a, b;
    scan(a, b);

    int ans;

    if (a % 3 + b % 3 == 0) {
        foreach (i ; a .. b + 1) {
            if (i % 3 == 0) {
                ans++;
            }
        }
    }
    else if ((a % 3 + b % 3) % 3 == 1) {
        foreach (i ; a .. b + 1) {
            if (i % 3 == 2) {
                ans++;
            }
        }
    }
    else {
        foreach (i ; a .. b + 1) {
            if (i % 3 == 1) {
                ans++;
            }
        }
    }

    writeln(ans);
}




void scan(T...)(ref T args) {
    import std.stdio : readln;
    import std.algorithm : splitter;
    import std.conv : to;
    import std.range.primitives;

    auto line = readln().splitter();
    foreach (ref arg; args) {
        arg = line.front.to!(typeof(arg));
        line.popFront();
    }
    assert(line.empty);
}



void fillAll(R, T)(ref R arr, T value) {
    static if (is(typeof(arr[] = value))) {
        arr[] = value;
    }
    else {
        foreach (ref e; arr) {
            fillAll(e, value);
        }
    }
}