#include <fstream>
using namespace std;
ifstream cin("orase.in");
ofstream cout("orase.out");
int main() {

    long long M, N;
    cin>>M>>N;

    long long D, L;     // D = distanta strazii lăturalnice față de capatul stang
                        // L = lungimea strazii laturalnice pâna la oras


    long long max1 = -9000000000000000LL;
    long long min1 =  9000000000000000LL;

    long long max2 = -9000000000000000;
    long long min2 =  9000000000000000;
    for (long long i = 0; i < N; i++) {

        cin>>D>>L;          //

        long long expr1 = D + L;
        long long expr2 = D - L;

        if (expr1 > max1) max1 = expr1;
        if (expr1 < min1) min1 = expr1;

        if (expr2 > max2) max2 = expr2;
        if (expr2 < min2) min2 = expr2;
    }

    long long ans1 = max1 - min1;
    long long ans2 = max2 - min2;

    long long ans;
    if (ans1 > ans2) ans = ans1;
    else ans = ans2;

    cout << ans;
    return 0;
}