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| #include <bits/stdc++.h>
#define FAST_IO
#ifdef FAST_IO
const int IN_LEN = 1000, OUT_LEN = 1000;
inline int nextChar() {
static char buf[IN_LEN], *h, *t;
if (h == t) {
t = (h = buf) + fread(buf, 1, IN_LEN, stdin);
if (h == t) return -1;
}
return *h++;
}
template<class T>
inline bool read(T &x) {
static bool iosig = 0;
static char c;
for (iosig = 0, c = nextChar(); !isdigit(c); c = nextChar()) {
if (c == -1) return false;
if (c == '-') iosig = 1;
}
for (x = 0; isdigit(c); c = nextChar()) x = (x << 1) + (x << 3) + (c ^ '0');
if (iosig) x = -x;
return true;
}
char obuf[OUT_LEN], *oh = obuf;
inline void writeChar(const char c) {
if (oh == obuf + OUT_LEN) fwrite(obuf, 1, OUT_LEN, stdout), oh = obuf;
*oh++ = c;
}
template<class T>
inline void write(T x) {
static int buf[30], cnt;
if (!x) writeChar(48);
else {
if (x < 0) writeChar('-'), x = -x;
for (cnt = 0; x; x /= 10) buf[++cnt] = x % 10 + 48;
while (cnt) writeChar(buf[cnt--]);
}
}
inline void flush() { fwrite(obuf, 1, oh - obuf, stdout); }
#endif
const int MAXN = 5005;
std::vector<int> edge[MAXN];
std::stack<int> st;
int dfn[MAXN], low[MAXN], idx, id[MAXN], scc;
inline void init() {
while (!st.empty()) st.pop();
idx = 0, scc = 1;
memset(id, -1, sizeof(id));
memset(edge, 0, sizeof(edge));
memset(dfn, -1, sizeof(dfn));
memset(low, -1, sizeof(low));
}
inline void addEdge(const int u, const int v) {
edge[u].push_back(v);
edge[v].push_back(u);
}
inline void tarjan(int u, int fa) {
dfn[u] = low[u] = ++idx, st.push(u);
bool flag = 0;
for (register int i = 0; i < edge[u].size(); i++) {
register int v = edge[u][i];
if (v == fa && !flag) {
flag = 1;
continue;
}
if (dfn[v] == -1) tarjan(v, u), low[u] = std::min(low[u], low[v]);
else low[u] = std::min(low[u], dfn[v]);
}
if (low[u] == dfn[u]) {
register int v;
do v = st.top(), id[v] = scc, st.pop(); while (!st.empty() && v != u);
scc++;
}
}
inline void solve(const int n, int &ans) {
register int u, v;
static int deg[MAXN];
memset(deg, 0, sizeof(deg));
for (register int i = 1; i <= n; i++) {
for (register int j = 0; j < edge[i].size(); j++) {
u = i, v = edge[i][j];
if (id[u] == id[v]) continue;
else deg[id[v]]++, deg[id[u]]++;
}
}
register int sum = 0;
for (register int i = 1; i < scc; i++)
if (deg[i] == 2)
sum++;
ans = sum + 1 >> 1;
}
int main() {
#ifndef ONLINE_JUDGE
freopen("in.in", "r", stdin);
#endif
register int n, m;
while (read(n), read(m)) {
init();
register int u, v;
for (register int i = 0; i < m; i++) read(u), read(v), addEdge(u, v);
tarjan(1, 1);
register int ans;
solve(n, ans);
write(ans), writeChar('\n');
}
flush();
return 0;
}
|
