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);

    a.sort();
    
    //Create Buckets and Remove Duplicates
    var buckets = [];
    for(var i = n-1; i >=0; i--){
        buckets[a[i]] = buckets[a[i]] || 0;
        buckets[a[i]]++;
        if(buckets[a[i]] > 1){
            a.splice(i,1)
        }
    }
    var longestRun = 0;
    var run = 0;
    var prevNums = [];
    for(var num in buckets){
        var ida = prevNums[0];
        var idb = prevNums[1];
        run = 0;
        if(ida && ida>num-2 && buckets[ida])run+=buckets[ida];
        if(idb && idb>num-2 && buckets[idb])run+=buckets[idb];
        if(num && buckets[num])run+=buckets[num];
        if(run > longestRun) longestRun=run;
        prevNums = [idb,num];
    }
    
    console.log(longestRun);
}