// tested by Hightail - https://github.com/dj3500/hightail
import std.stdio, std.string, std.conv, std.algorithm;
import std.range, std.array, std.math, std.typecons, std.container, core.bitop;

immutable mod = 10^^9 + 7;
immutable inf = 10^^9 + 7;

void main() {
    int n;
    int[] a;
    scan(n);
    a = readln.split.to!(int[]);

    auto cnt = new int[](200000);

    foreach (ai ; a) {
        cnt[ai]++;
    }

    int ans;

    foreach (i ; 0 .. 100000) {
        int b = cnt[i] + cnt[i + 1] + cnt[i + 2];
        ans = max(ans, b);
    }

    writeln(ans);
}



void scan(T...)(ref T args) {
    string[] line = readln.split;
    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);
        }
    }
} 