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; }
real readReal() { return readToken.to!real; }

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)); }



int[] A, B;
int[][] G;

bool[] vis;
int[] pari;
int[] ans;

bool dfs(int u, int ip) {
  vis[u] = true;
  pari[u] = ip;
  foreach (i; G[u]) {
    if (i != ip) {
      const v = A[i] ^ B[i] ^ u;
      if (vis[v]) {
        ans ~= i;
        for (int w = u; w != v; ) {
          const j = pari[w];
          ans ~= j;
          w = A[j] ^ B[j] ^ w;
        }
        return true;
      }
      if (dfs(v, i)) {
        return true;
      }
    }
  }
  return false;
}

void main() {
  try {
    for (; ; ) {
      readLong();
      readLong();
      const M = readInt();
      long[] X = new long[M];
      long[] Y = new long[M];
      foreach (i; 0 .. M) {
        X[i] = readLong();
        Y[i] = readLong();
      }
      
      const xs = X.dup.sort.uniq.array;
      const ys = Y.dup.sort.uniq.array;
      const xsLen = cast(int)(xs.length);
      const ysLen = cast(int)(ys.length);
      A = new int[M];
      B = new int[M];
      foreach (i; 0 .. M) {
        A[i] = xs.lowerBound(X[i]);
        B[i] = xsLen + ys.lowerBound(Y[i]);
      }
      G = new int[][xsLen + ysLen];
      foreach (i; 0 .. M) {
        G[A[i]] ~= i;
        G[B[i]] ~= i;
      }
      
      vis = new bool[xsLen + ysLen];
      pari = new int[xsLen + ysLen];
      pari[] = -1;
      ans = null;
      foreach (u; 0 .. xsLen + ysLen) {
        if (!vis[u]) {
          if (dfs(u, -1)) {
            break;
          }
        }
      }
      
      if (ans) {
        if (Y[ans[0]] != Y[ans[1]]) {
          ans = ans[1 .. $] ~ ans[0];
        }
        
        writeln(ans.length);
        foreach (index, i; ans) {
          if (index > 0) write(" ");
          write(i + 1);
        }
        writeln;
      } else {
        writeln(-1);
      }
    }
  } catch (EOFException e) {
  }
}