import sys
sys.setrecursionlimit(1000000)
input = sys.stdin.buffer.readline

def main():
    H,W,N = map(int,input().split())
    dic = {}
    Start = set([])
    G = [[] for _ in range(H+W)]
    for i in range(N):
        x,y = map(int,input().split())
        x -= 1; y -= 1
        dic[(x,y+H)] = i+1 #1-index
        h = x
        w = y + H
        G[h].append(w)
        G[w].append(h)
        Start.add(h)
    #print(G)
    #print(dic)
    def ans_print(X):
        #print("X",X)
        ret = []
        for i in range(len(X)):
            if i == len(X) - 1: #最後
                a = X[i]; b = X[0]
            else:
                a = X[i]; b = X[i+1]
            if a > b:
                a,b = b,a
            ret.append(dic[(a,b)])
        print(len(ret))
        print(*ret)
        exit()

    def dfs(v):
        stack.append(v)
        visited[v] = len(stack) - 1 #stackの何番目にいるか
        for u in G[v]:
            if visited[u] != -1 and len(stack) - visited[u] > 2:
                ans_print(stack[visited[u]:])
            if visited[u] != -1: continue
            #stack.append(u)
            dfs(u)
            stack.pop()
            visited[u] = -1

    used = set([])
    for i in Start:
        if i in used: continue
        stack = []
        visited = [-1]*(H+W)
        dfs(i)
        used.add(i)
        #print("NEXT",stack)
    print(-1)
        
if __name__ == '__main__':
    main()