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

var input_stdin = "";
var input_stdin_array = "";
var input_currentline = 0;

process.stdin.on('data', function (data) {
    input_stdin += data;
});

process.stdin.on('end', function () {
    input_stdin_array = input_stdin.split("\n");
    main();    
});

function readLine() {
    return input_stdin_array[input_currentline++];
}

/////////////// ignore above this line ////////////////////

function main() {
    var n = parseInt(readLine());
    a = readLine().split(' ');
    a = a.map(Number);
    var numMap = new Map();
    for (let n of a)
        if (numMap.has(n))
            numMap.set(n, numMap.get(n) + 1);
        else
            numMap.set(n, 1);
    var largest = 0;
    for (let [num, times] of numMap) {
        if (times > largest)
            largest = times;
        if (numMap.has(num - 1) && numMap.get(num - 1) + times > largest)
            largest = numMap.get(num - 1) + times;
        if (numMap.has(num + 1) && numMap.get(num + 1) + times > largest)
            largest = numMap.get(num + 1) + times;
    }
    process.stdout.write(largest + "\n");
    //a.sort(function (a, b) { if (a < b) return -1; if (a == b) return 0; else return 1; });
}