#include <bits/stdc++.h>
#define ll long long
#define enl putchar('\n')
#define all(x) (x).begin(),(x).end()
#define debug(x) printf(" "#x":%d\n",x);
using namespace std;
const int MAXN = 2e5 + 5;
const int inf = 0x3f3f3f3f;
const ll INF = 0x3f3f3f3f3f3f3f3f;
const int mod = 998244353;
typedef pair<int, int> pii;
char buf[1 << 21], * p1 = buf, * p2 = buf, obuf[1 << 21], * o = obuf, of[35];
#define gc()(p1==p2&&(p2=(p1=buf)+fread(buf,1,1<<21,stdin),p1==p2)?EOF:*p1++)
inline ll qpow(ll a, ll n) { ll res = 1; while (n) { if (n & 1)res = res * a % mod; n >>= 1; a = a * a % mod; }return res; }
template <class T = int>inline T read() { T s = 0, f = 1; char c = gc(); for (; !isdigit(c); c = gc())if (c == '-')f = -1; for (; isdigit(c); c = gc())s = s * 10 + c - '0'; return s * f; }
inline void read(int* a, int n) { for (int i = 1; i <= n; ++i)a[i] = read(); }
inline int inal(char* s) { int n = 0; for (s[0] = gc(); !isalpha(s[0]); s[0] = gc()); for (; isalpha(s[n]); s[++n] = gc()); return s[n] = 0, n; }
inline int indi(char* s) { int n = 0; for (s[0] = gc(); !isdigit(s[0]); s[0] = gc()); for (; isdigit(s[n]); s[++n] = gc()); return s[n] = 0, n; }
inline void outd(auto* a, int n) { for (int i = 1; i <= n; ++i)printf("%d ", a[i]); enl; }
int n, m, q;
int L, R;

struct EG {
    int to, nxt;
}e[MAXN << 1];
int head[MAXN], etot;
inline void add(int u, int v) {
    e[etot] = EG {v, head[u]};
    head[u] = etot++;
}
void clear(int n = MAXN - 1) { memset(head + 1, -1, sizeof(int) * n); etot = 0; }
int mat[MAXN], vis[MAXN], TC;

bool dfs(int cur) {
    for (int i = head[cur]; ~i; i = e[i].nxt) {
        int to = e[i].to;
        if (vis[to] != TC) {
            vis[to] = TC;
            if (mat[to] == 0 || dfs(mat[to])) {
                mat[to] = cur;
                return 1;
            }
        }
    }
    return 0;
}

void solve() {
    L = read(), R = read(), m = read();
    clear(max(L, R));
    for (int i = 1; i <= m; ++i) {
        int u = read() + 1, v = read() + 1;
        add(u, v);
    }
    int cnt = 0;
    for (int i = 1; i <= L; ++i) ++TC, dfs(i);
    for (int i = 1; i <= R; ++i)cnt += (mat[i] != 0);
    printf("%d\n", cnt);
    for (int i = 1; i <= R; ++i)
        if (mat[i])printf("%d %d\n", mat[i] - 1, i - 1);
}
signed main(signed argc, char const* argv[]) {
    clock_t c1 = clock();
#ifdef LOCAL
    freopen("in.in", "r", stdin);
    freopen("out.out", "w", stdout);
#endif
    //=============================================================
    int TxT = 1;
    // TxT = read();
    while (TxT--)
        solve();
    //=============================================================
#ifdef LOCAL
    end :
    cerr << "Time Used:" << clock() - c1 << "ms" << endl;
#endif
    return 0;
}