#include <bits/stdc++.h>
using namespace std;
inline int read() {
  int x = 0, f = 1;
  char ch = getchar();
  while (ch < '0' || ch > '9') {
    if (ch == '-') f = -1;
    ch = getchar();
  }
  while (ch >= '0' && ch <= '9') {
    x = x * 10 + ch - '0';
    ch = getchar();
  }
  return x * f;
}
const int MAXN = 1003, MAXM = 300005;
int n, m, l, a[MAXM], b[MAXM], c[MAXM], d[MAXM], e[MAXM];
long long f[26][MAXN][MAXN], s[MAXN][MAXN], g[MAXN][MAXN], h[MAXN][MAXN];
int main() {
  int i, j, k;
  n = read();
  m = read();
  l = read();
  for (i = 1; i <= n; ++i) {
    for (j = 1; j <= m; ++j) s[i][j] = getchar() - 'a';
    getchar();
  }
  memset(f, 0, sizeof(f));
  for (i = 1; i <= l; ++i) {
    a[i] = read();
    b[i] = read();
    c[i] = read();
    d[i] = read();
    e[i] = getchar() - 'a';
    f[e[i]][a[i]][b[i]]++;
    f[e[i]][a[i]][d[i] + 1]--;
    f[e[i]][c[i] + 1][b[i]]--;
    f[e[i]][c[i] + 1][d[i] + 1]++;
  }
  for (k = 0; k < 26; ++k)
    for (i = 1; i <= n; ++i)
      for (j = 1; j <= m; ++j)
        f[k][i][j] += f[k][i - 1][j] + f[k][i][j - 1] - f[k][i - 1][j - 1];
  memset(g, 0, sizeof(g));
  for (i = 1; i <= n; ++i)
    for (j = 1; j <= m; ++j) {
      for (k = 0; k < 26; ++k) g[i][j] += fabs(k - s[i][j]) * f[k][i][j];
      g[i][j] += g[i - 1][j] + g[i][j - 1] - g[i - 1][j - 1];
    }
  memset(h, 0, sizeof(h));
  for (i = 1; i <= l; ++i) {
    h[a[i]][b[i]]++;
    h[a[i]][d[i] + 1]--;
    h[c[i] + 1][b[i]]--;
    h[c[i] + 1][d[i] + 1]++;
  }
  for (i = 1; i <= n; ++i)
    for (j = 1; j <= m; ++j) {
      h[i][j] += h[i - 1][j] + h[i][j - 1] - h[i - 1][j - 1];
      f[s[i][j]][i][j] += l - h[i][j];
    }
  for (k = 0; k < 26; ++k)
    for (i = 1; i <= n; ++i)
      for (j = 1; j <= m; ++j)
        f[k][i][j] += f[k][i - 1][j] + f[k][i][j - 1] - f[k][i - 1][j - 1];
  long long tmp, ans = 1000000000000000000LL;
  for (i = 1; i <= l; ++i) {
    tmp = g[n][m] - (g[c[i]][d[i]] - g[a[i] - 1][d[i]] - g[c[i]][b[i] - 1] +
                     g[a[i] - 1][b[i] - 1]);
    for (k = 0; k < 26; ++k) {
      tmp += fabs(k - e[i]) * (f[k][c[i]][d[i]] - f[k][a[i] - 1][d[i]] -
                               f[k][c[i]][b[i] - 1] + f[k][a[i] - 1][b[i] - 1]);
    }
    ans = min(ans, tmp);
  }
  cout << ans << endl;
  return 0;
}
