#include <queue>
#include <vector>
#include <cstdio>
#include <cassert>
#include <algorithm>

using namespace std;

const int N = 200050;

int p, r, t, a[510], m[510][510], s[510][510], b[510], u[N], v[N];
bool vis[510];

bool check(int mid) {
    queue <int> q;
    for (int i = 0; i < p; i++) {
        vis[i] = false;
        for (int j = 0; j < r; j++) {
            s[i][j] = m[i][j];
        }
    }
    for (int i = 0; i < r; i++) {
        b[i] = a[i];
    }
    for (int i = 0; i <= mid; i++) {
        b[v[i]]--;
        s[u[i]][v[i]]--;
        assert(u[i] < p);
        assert(v[i] < r);
        //assert(b[v[i]] >= 0);
        assert(s[u[i]][v[i]] >= 0);
    }
    //printf("debg %d ..\n", mid);
    for (int i = 0; i < p; i++) {
        for (int j = 0; j < r; j++) {
            //printf("%d ", s[i][j]);
        }
        //puts("");
    }
    for (int i = 0; i < p; i++) {
        bool ok = true;
        bool eq = true;
        for (int j = 0; j < r; j++) {
            if (s[i][j] != 0) {
                eq = false;
                break;
            }
        }
        for (int j = 0; j < r; j++) {
            if (s[i][j] > b[j]) {
                ok = false;
                break;
            }
        }
        if (ok || eq) {
            vis[i] = true;
            q.push(i);
        }
    }
    while (!q.empty()) {
        int now = q.front();
        q.pop();
        for (int i = 0; i < r; i++) {
            b[i] += m[now][i] - s[now][i];
        }
        for (int i = 0; i < p; i++) {
            if (vis[i]) {
                continue;
            }
            bool ok = true;
            bool eq = true;
            for (int j = 0; j < r; j++) {
                if (s[i][j] != 0) {
                    eq = false;
                    break;
                }
            }
            for (int j = 0; j < r; j++) {
                if (s[i][j] > b[j]) {
                    ok = false;
                    break;
                }
            }
            if (ok || eq) {
                vis[i] = true;
                q.push(i);
            }
        }
    }
    for (int i = 0; i < p; i++) {
        if (!vis[i]) {
            return false;
        }
    }
    return true;
}

int main() {

    while (scanf("%d %d %d", &p, &r, &t) != EOF) {
        for (int i = 0; i < r; i++) {
            scanf("%d", &a[i]);
        }
        for (int i = 0; i < p; i++) {
            for (int j = 0; j < r; j++) {
                scanf("%d", &m[i][j]);
            }
        }
        for (int i = 0; i < t; i++) {
            scanf("%d %d", &u[i], &v[i]);
            u[i]--;
            v[i]--;
        }
        if (check(t - 1)) {
            puts("-1");
            continue;
        }
        int lo = -1;
        int hi = t - 1;
        for (int i = 0; i + 1 < t && i < 100; i++) {
            //printf("%d %d %d\n", i, check(i), check(i + 1));
            //assert(check(i) >= check(i + 1));
        }
        while (lo <= hi) {
            int mid = (lo + hi) / 2;
            if (check(mid)) {
                lo = mid + 1;
            } else {
                hi = mid - 1;
            }
        }
        printf("%d\n", lo + 1);
    }

    return 0;

}

Measured memory_bytes: 5396