import std.conv, std.functional, std.range, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.bitmanip, std.complex, std.container, std.math, std.mathspecial, std.numeric, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; }
int readInt() { return readToken.to!int; }
long readLong() { return readToken.to!long; }

string COLOR(string s = "") { return "\x1b[" ~ s ~ "m"; }

bool chmin(T)(ref T t, in T f) { if (t > f) { t = f; return true; } else { return false; } }
bool chmax(T)(ref T t, in T f) { if (t < f) { t = f; return true; } else { return false; } }

int binarySearch(alias pred, T)(in T[] as) { int lo = -1, hi = cast(int)(as.length); for (; lo + 1 < hi; ) { const mid = (lo + hi) >> 1; (unaryFun!pred(as[mid]) ? hi : lo) = mid; } return hi; }
int lowerBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a >= val)); }
int upperBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a > val)); }


enum K = 5;

void main() {
  try {
    for (; ; ) {
      const N = readInt;
      const M = readInt;
      auto X = new int[M*N];
      auto Y = new int[M*N];
      foreach (i; 0 .. M*N) {
        Y[i] = readInt - 1;
        X[i] = readInt - 1;
      }
      
      auto posss = new int[][](M, N + 1);
      foreach (i; 0 .. M*N) {
        posss[X[i]][Y[i]] = i;
      }
      foreach (x; 0 .. M) {
        posss[x][N] = posss[x][0];
      }
      
      int ans = int.max;
      auto ps = new int[K];
      foreach (x; 0 .. M) {
        foreach (y; 0 .. N - 4 + 1) {
          static foreach (dy; 0 .. K) {
            ps[dy] = posss[x][y + dy];
          }
          ps.sort;
          int cost;
          int cur = K;
          for (; ; ) {
            const k = ps.lowerBound(cur);
            if (k == K) {
              break;
            }
            // ps[k] < cur + (K-k) x
            const need = (ps[k] - cur) / (K - k) + 1;
            cost += need;
            cur += (K - k) * need;
            assert(ps[k] < cur, format("ps = %s, cost = %s, cur = %s, k = %s, need = %s", ps, cost, cur, k, need));
          }
          debug {
            writeln(ps, ": ", cost);
          }
          chmin(ans, cost);
        }
      }
      writeln(ans);
    }
  } catch (EOFException e) {
  }
}