#include <algorithm>
#include <cstdint>
#include <iostream>
#include <queue>
#include <set>
#include <utility>
#include <vector>

int main() {
    int64_t stations, lineNum;
    std::cin >> stations >> lineNum;
    std::vector<std::set<int64_t>> lines(lineNum);
    for (int64_t i = 0; i < lineNum; ++i) {
        int64_t stInLine;
        std::cin >> stInLine;
        for (int64_t j = 0; j < stInLine; ++j) {
            int64_t curStat;
            std::cin >> curStat;
            lines[i].insert(curStat);
        }
    }
    int64_t from, to;
    std::cin >> from >> to;
    std::set<int64_t> reach = {from};
    for (int64_t i = 0; i < lineNum; ++i) {
        std::set<int64_t> newReach = reach;
        for (int64_t j = 0; j < lineNum; j++) {
            std::set<int64_t> inter;
            std::set_intersection(std::begin(lines[j]), std::end(lines[j]), std::begin(reach),
                                  std::end(reach), std::inserter(inter, std::begin(inter)));
            if (!inter.empty()) {
                std::set_union(std::begin(lines[j]), std::end(lines[j]), std::begin(newReach),
                               std::end(newReach), std::inserter(newReach, std::begin(newReach)));
            }
        }
        reach = newReach;
        if (reach.find(to) != std::end(reach)) {
            std::cout << i << '\n';
            return 0;
        }
    }
    std::cout << -1 << '\n';
    return 0;
}