185.cpp

#pragma GCC diagnostic ignored "-Wunused-result"

#include <stdio.h>
#include <bits/stdc++.h>

int main() {
    int n, curr; std::cin >> n >> curr;
    std::vector<std::vector<char>> faster(1+n, std::vector<char>(1+n, -1));
    int a, b;
    while (scanf("%d %d", &a, &b) == 2) {
        faster[a][b] = true;
        faster[b][a] = false;
    }
    bool flag = true;
    while (flag) {
        flag = false;
        for (int a = 1; a <= n; ++a) {
            for (int b = 1; b <= n; ++b) {
                if (faster[a][b] > -1) continue;
                for (int c = 1; c <= n; ++c) {
                    if (faster[a][c] == 1 && faster[c][b] == 1) {
                        faster[a][b] = 1;
                        faster[b][a] = 0;
                        flag = true;
                        break;
                    }
                }
            }
        }
    }
    for (int i = 1; i <= n; ++i) {
        if (curr != i && (faster[curr][i] == -1 || faster[curr][i] == 0)) {
            std::cout << "No" << std::endl; return 0;
        }
    }
    std::cout << "Yes" << std::endl;
    return 0;
}