#include<stdio.h>
using namespace std;
const int N = 50005;
struct orase
{
    int x, y;
};
orase v[N];
int abs (int x)
{
    if (x < 0)
        return -x;
    return x;
}
int main ()
{
    FILE *in, *out;
    in = fopen ("orase.in", "r");
    out = fopen ("orase.out", "w");
    int n, m;
    fscanf (in, "%d%d", &m, &n);
    int i;
    for (i = 1; i <= n; i++)
        fscanf (in, "%d%d", &x[i], &y[i]);
    int ic1, ic2;
    int maxim = abs (x[1] - x[2]) + y[1] + y[2];
    ic1 = 1;
    ic2 = 2;
    int aux1, aux2;
    for (i = 3; i <= n; i++)
    {
        aux1 = abs (x[ic1] - x[i]) + y[ic1] + y[i];
        aux2 = abs (x[ic2] - x[i]) + y[ic2] + y[i];
        if (aux1 >= aux2 && aux1 > maxim)
        {
            maxim = aux1;
            ic2 = i;
        }
        if (aux2 >= aux1 && aux1 > maxim)
        {
            maxim = aux2;
            ic1 = i;
        }
    }
    fprintf (out, "%d", maxim);
    return 0;
}