import threading, sys
def main():
n, m = map(int, input().split())
graph = [[] for _ in range(n)]
for _ in range(m):
u, v = map(int, input().split())
graph[u - 1].append(v)
graph[v - 1].append(u)
visited = [False for _ in range(n)]
def check(node):
nonlocal cycle
visited[node - 1] = True
if len(graph[node - 1]) != 2:
cycle = False
for neighbor in graph[node - 1]:
if not visited[neighbor-1]:
check(neighbor)
ans = 0
for n in range(n):
if not visited[n]:
node = n + 1
cycle = True
check(node)
if cycle:
ans += 1
print(ans)
if __name__ == '__main__':
sys.setrecursionlimit(1 << 30)
threading.stack_size(1 << 27)
main_thread = threading.Thread(target=main)
main_thread.start()
main_thread.join()#include <bits/stdc++.h>
#define int long long
#define endl '\n'
#define pii pair<int,int>
#define vint vector<int>
#define vpii vector<pii>
#define fi first
#define se second
#define pb push_back
#define all(x) x.begin(), x.end()
#define unmap unordered_map
#define graph vector<vint>
#define clr(x) memset(x,0,sizeof(x));
using namespace std;
const int N = (int)2e5 + 69;
const int mod = (int)1e4 + 7;
int INF = INT_MAX;
int power(int a, int b) { int ans = 1; while (b) { if (b % 2) ans *= a; a *= a; b /= 2; } return ans; }
int gcd(int a, int b) { if (b == 0)return a;return gcd(b, a % b); }
graph g;
int vis[N];
int road[N];
bool tmp = 1;
void dfs(int node) {
vis[node] = 1;
if (g[node].size() != 2)
tmp = 0;
for (int c : g[node])
if (!vis[c])
dfs(c);
return;
}
int messi = 10, cr7 = 7;
int32_t main() {
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
int n, m;
cin >> n >> m;
g.resize(n + 1);
for (int i = 0; i < m; i++) {
int a, b;
cin >> a >> b;
g[a].pb(b);
g[b].pb(a);
}
int ans = 0;
for (int i = 1; i <= n; i++) {
if (!vis[i]) {
dfs(i);
ans += tmp;
tmp = 1;
}
}
cout << ans << endl;
}310. Minimum Height Trees | 2110. Number of Smooth Descent Periods of a Stock |
2109. Adding Spaces to a String | 2108. Find First Palindromic String in the Array |
394. Decode String | 902. Numbers At Most N Given Digit Set |
221. Maximal Square | 1200. Minimum Absolute Difference |
1619B - Squares and Cubes | 1619A - Square String |
1629B - GCD Arrays | 1629A - Download More RAM |
1629C - Meximum Array | 1629D - Peculiar Movie Preferences |
1629E - Grid Xor | 1629F1 - Game on Sum (Easy Version) |
2148. Count Elements With Strictly Smaller and Greater Elements | 2149. Rearrange Array Elements by Sign |
2150. Find All Lonely Numbers in the Array | 2151. Maximum Good People Based on Statements |
2144. Minimum Cost of Buying Candies With Discount | Non empty subsets |
1630A - And Matching | 1630B - Range and Partition |
1630C - Paint the Middle | 1630D - Flipping Range |
1328A - Divisibility Problem | 339A - Helpful Maths |
4A - Watermelon | 476A - Dreamoon and Stairs |