#include <bits/stdc++.h>
using namespace std;
const long long N = 1e3 + 5;
const long long Q = 3e5 + 5;
char w[N][N];
char x[Q];
long long l[Q], r[Q];
long long u[Q], d[Q];
long long f[N][N];
long long c[N][N][26];
signed main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  long long n;
  cin >> n;
  long long m;
  cin >> m;
  long long k;
  cin >> k;
  for (long long i = 1; i <= n; ++i)
    for (long long j = 1; j <= m; ++j) cin >> w[i][j];
  for (long long i = 1; i <= k; ++i) {
    cin >> l[i] >> u[i];
    cin >> r[i] >> d[i];
    cin >> x[i];
    x[i] -= 'a';
    ++r[i];
    ++d[i];
    c[l[i]][u[i]][x[i]]++;
    c[l[i]][d[i]][x[i]]--;
    c[r[i]][u[i]][x[i]]--;
    c[r[i]][d[i]][x[i]]++;
  }
  for (long long i = 1; i <= n; ++i)
    for (long long j = 1; j <= m; ++j)
      for (long long t = 0; t < 26; ++t)
        c[i][j][t] -= c[i - 1][j - 1][t], c[i][j][t] += c[i - 1][j][t],
            c[i][j][t] += c[i][j - 1][t];
  for (long long i = 1; i <= n; ++i)
    for (long long j = 1; j <= m; ++j) {
      c[i][j][w[i][j] - 'a'] = k;
      for (long long t = 0; t < 26; ++t)
        if (t != w[i][j] - 'a') c[i][j][w[i][j] - 'a'] -= c[i][j][t];
      for (long long t = 0; t < 26; ++t)
        f[i][j] += c[i][j][t] * abs(w[i][j] - 'a' - t);
    }
  for (long long i = 1; i <= n; ++i)
    for (long long j = 1; j <= m; ++j) {
      f[i][j] -= f[i - 1][j - 1];
      f[i][j] += f[i - 1][j];
      f[i][j] += f[i][j - 1];
      for (long long t = 0; t < 26; ++t)
        c[i][j][t] -= c[i - 1][j - 1][t], c[i][j][t] += c[i - 1][j][t],
            c[i][j][t] += c[i][j - 1][t];
    }
  long long ans = 1e18;
  for (long long i = 1; i <= k; ++i) {
    l[i]--;
    r[i]--;
    u[i]--;
    d[i]--;
    long long cur = f[n][m];
    cur -= f[r[i]][d[i]];
    cur += f[r[i]][u[i]];
    cur += f[l[i]][d[i]];
    cur -= f[l[i]][u[i]];
    for (long long t = 0; t < 26; ++t)
      cur += (c[r[i]][d[i]][t] - c[r[i]][u[i]][t] - c[l[i]][d[i]][t] +
              c[l[i]][u[i]][t]) *
             abs(x[i] - t);
    ans = min(ans, cur);
  }
  cout << ans << endl;
}
