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;
}1031A - Golden Plate | 1559C - Mocha and Hiking |
427B - Prison Transfer | 330A - Cakeminator |
426A - Sereja and Mugs | 363A - Soroban |
1585C - Minimize Distance | 1506E - Restoring the Permutation |
1539A - Contest Start | 363D - Renting Bikes |
1198D - Rectangle Painting 1 | 1023B - Pair of Toys |
1725A - Accumulation of Dominoes | 1675E - Replace With the Previous Minimize |
839A - Arya and Bran | 16B - Burglar and Matches |
1625B - Elementary Particles | 1725G - Garage |
1725B - Basketball Together | 735A - Ostap and Grasshopper |
1183B - Equalize Prices | 1481A - Space Navigation |
1437B - Reverse Binary Strings | 1362B - Johnny and His Hobbies |
1299A - Anu Has a Function | 1111A - Superhero Transformation |
954A - Diagonal Walking | 39F - Pacifist frogs |
1451C - String Equality | 386A - Second-Price Auction |