#include <stdio.h>

#pragma GCC optimize("Ofast")
#pragma GCC optimize ("unroll-loops")

static inline int min( int a, int b ) {
    return ( a <= b ? a : b );
}

static inline int max( int a, int b ) {
    return ( a >= b ? a : b );
}

int d, l, a, b;

int main()
{
    FILE *fin = fopen( "orase.in", "r" );
    for( fscanf( fin, "%d%d", &d, &l ); ~fscanf( fin, "%d%d", &d, &l ); a = max( a, d + l ), b = max( b, l - d ) );
    fclose( fin );

    FILE *fout = fopen( "orase.out", "w" );
    fprintf( fout, "%d\n", a + b );
    fclose( fout );
    return 0;
}