function solution(K, J) {
    const diff = Math.abs(K - J);
    const max = Math.max(K, J);
    const result = max - diff;
    if (result === 0)
        console.log(0);
    else
        console.log(Math.floor((result *2) / 3));
}

function main() {
    // write your code here.
    // call functions `nextString`, `nextFloat` and `nextInt`
    // to read the next token of input (ignoring whitespace)
    // Alternatively, you can create your own input parser functions
    // use console.log() to write to stdout

    var K = nextInt();
    var J = nextInt();
    solution(K, J);
    // var s = nextString();
    // var c = nextChar();
    // var f = nextFloat();
}

// default parsers for JS.
function nextInt() {
    return parseInt(nextString());
}

function nextFloat() {
    return parseFloat(nextString());
}

function nextString() {
    var next_string = "";
    clearWhitespaces();
    while (input_cursor < input_stdin.length && !isWhitespace(input_stdin[input_cursor])) {
        next_string += input_stdin[input_cursor];
        input_cursor += 1;
    }
    return next_string;
}

function nextChar() {
    clearWhitespaces();
    if (input_cursor < input_stdin.length) {
        return input_stdin[input_cursor++];
    } else {
        return '\0';
    }
}

process.stdin.resume();
process.stdin.setEncoding('ascii');

var input_stdin = "";
var input_cursor = 0;
process.stdin.on('data', function (data) {
    input_stdin += data;
});
process.stdin.on('end', function () {
    main();
});

function isWhitespace(character) {
    return ' \t\n\r\v'.indexOf(character) > -1;
}

function clearWhitespaces() {
    while (input_cursor < input_stdin.length && isWhitespace(input_stdin[input_cursor])) {
        // ignore the next whitespace character
        input_cursor += 1;
    }
}