#include <bits/stdc++.h>
using namespace std;
long long tag[26][1010][1010], A[1010][1010];
long long a[300100], b[300100], c[300100], d[300100], n, m, p, col[300100];
long long base, ans = 1ll << 60, now, ps[1010][1010];
char ch[2], str[1010][1010];
int main() {
  scanf("%lld%lld%lld", &n, &m, &p);
  for (int i = 1; i <= n; ++i) scanf("%s", str[i] + 1);
  for (int i = 1; i <= p; ++i) {
    scanf("%lld%lld%lld%lld%s", &a[i], &b[i], &c[i], &d[i], ch);
    col[i] = ch[0] - 'a';
    tag[ch[0] - 'a'][a[i]][b[i]]++;
    tag[ch[0] - 'a'][a[i]][d[i] + 1]--;
    tag[ch[0] - 'a'][c[i] + 1][b[i]]--;
    tag[ch[0] - 'a'][c[i] + 1][d[i] + 1]++;
    A[a[i]][b[i]]--;
    A[a[i]][d[i] + 1]++;
    A[c[i] + 1][b[i]]++;
    A[c[i] + 1][d[i] + 1]--;
    A[1][1]++;
  }
  for (int c = 0; c < 26; ++c)
    for (int i = 1; i <= n; i++)
      for (int j = 1; j <= m; ++j)
        tag[c][i][j] = tag[c][i - 1][j] + tag[c][i][j - 1] -
                       tag[c][i - 1][j - 1] + tag[c][i][j];
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= m; ++j)
      tag[str[i][j] - 'a'][i][j] +=
          (A[i][j] = A[i - 1][j] + A[i][j - 1] - A[i - 1][j - 1] + A[i][j]);
  for (int i = 1; i <= n; ++i)
    for (int j = 1; j <= m; ++j)
      for (int c = 0; c < 26; ++c)
        ps[i][j] += 1ll * tag[c][i][j] * abs(str[i][j] - 'a' - c);
  for (int i = 1; i <= n; ++i)
    for (int j = 1; j <= m; ++j)
      ps[i][j] = ps[i - 1][j] + ps[i][j - 1] - ps[i - 1][j - 1] + ps[i][j];
  for (int c = 0; c < 26; ++c)
    for (int i = 1; i <= n; i++)
      for (int j = 1; j <= m; ++j)
        tag[c][i][j] = tag[c][i - 1][j] + tag[c][i][j - 1] -
                       tag[c][i - 1][j - 1] + tag[c][i][j];
  for (int i = 1; i <= p; ++i) {
    long long now = ps[n][m] - (ps[c[i]][d[i]] - ps[a[i] - 1][d[i]] -
                                ps[c[i]][b[i] - 1] + ps[a[i] - 1][b[i] - 1]);
    for (int cx = 0; cx < 26; ++cx)
      now += 1ll * abs(cx - col[i]) *
             (tag[cx][c[i]][d[i]] - tag[cx][a[i] - 1][d[i]] -
              tag[cx][c[i]][b[i] - 1] + tag[cx][a[i] - 1][b[i] - 1]);
    ans = min(ans, now);
  }
  printf("%I64d", ans);
}
