import * as fs from 'fs';
let outputBuffer = '';
main();
flush();

function flush() {
    console.log(outputBuffer);
}

function print(out: string | number | bigint): void;
function print<T>(out: Array<T>, separator: string): void;
function print<T>(out: string | number | bigint | Array<T>, separator?: string) {
    if (Array.isArray(out)) {
        outputBuffer += out.join(separator);
    } else {
        outputBuffer += out;
    }
}
function println(out: string | number | bigint): void;
function println<T>(out: Array<T>, separator: string): void;
function println<T>(out: string | number | bigint | Array<T>, separator?: string) {
    if (Array.isArray(out)) {
        print(out, separator || '');
    } else {
        print(out);
    }
    print('\n');
}

function main() {
    const inputs = fs.readFileSync('/dev/stdin', 'utf8');
    const inputArray = inputs.split(/\s/);
    let in_a = Number(inputArray[0]);
    const in_b = Number(inputArray[1]);
    let res = 0;
    for (let i = in_a; i <= in_b; i++) {
        const ans = i + in_a + in_b;
        if (ans % 3 == 0) {
            res++;
        }
    }
    print(res);
    // MULTIPLE OUTPUT
    //for(let i = 0; i < N; ++i) {
    //  println(ans[i]);
    //}
}