func_code_string: #include <bits/stdc++.h>   using namespace std;   int n, m, in[100010], sum1, sum2;   int main() {     cin >> n >> m;     for (int i = 1; i <= m; i++) {       int x, y;       cin >> x >> y;       in[x]++;       in[y]++;     }     for (int i = 1; i <= n + 1; i++)       if (in[i] == 1)         sum1++;       else if (in[i] == 2)         sum2++;     if (sum1 == 2 && sum2 == n - 2) {       cout <<  bus topology ;       return 0;     }     sum1 = sum2 = 0;     for (int i = 1; i <= n; i++)       if (in[i] == 2) sum1++;     if (sum1 == n) {       cout <<  ring topology ;       return 0;     }     sum1 = sum2 = 0;     for (int i = 1; i <= n + 1; i++)       if (in[i] == 1)         sum1++;       else if (in[i] == n - 1)         sum2++;     if (sum1 == n - 1 && sum2 == 1) {       cout <<  star topology ;       return 0;     }     cout <<  unknown topology ;     return 0;   }   