#include <stdio.h>
#include <vector>
#include <unordered_map>
#include <algorithm>
using namespace std;

#define MAXM 1000010

struct arc_t {
    int m, f;
};

vector<arc_t> archi;
vector<arc_t> presi;

int N, M, F;


int main() {
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);

    scanf("%d%d%d", &M, &F, &N);

    for (int i = 0; i < N; i++) {
        int m, f;
        scanf("%d%d", &m, &f);
        archi.push_back({m, f});
    }

    vector<arc_t> tail(N);
    tail[0] = archi[0];
    int length = 1;

    for (int i = 0; i < N; i++) {
        /*
        printf("(%d, %d)\n", archi[i].m, archi[i].f);

        /// Mostro la sequenza corrente
        for (int j = 0; j < length; j++) {
            printf("[%d, %d]", tail[j].m, tail[j].f);
        }
        printf("\n");
        */

        if (max(archi[i].m, archi[i].f) < min(tail[0].m, tail[0].f)) {
            //printf("\tNuova sequenza\n");
            tail[0] = archi[i];
        }
        else if (min(archi[i].m, archi[i].f) > max(tail[length-1].m, tail[length-1].f)) {
            //printf("\tEstendo\n");
            tail[length++] = archi[i];
        }
        else {
            int lo = 0, hi = length-1;
            while (lo <= hi) {
                int mid = (lo+hi) / 2;
                /// Se tail[mid] si trova prima o si interseca con archi[i]
                if (max(tail[mid].m, tail[mid].f) <= min(archi[i].m, archi[i].f)) {
                    lo = mid + 1;
                }
                else {
                    hi = mid - 1;
                }
            }
            if (lo < length)
                tail[lo] = archi[i];
        }
        //printf("\n");
    }
    printf("%d\n", length*2);

    return 0;
}