732F Tourist Reform

 // CF 732F Tourist Reform
 // 思路：两遍tarjan
 // 找强联通分量
 #include <bits/stdc++.h>
 using namespace std;
 #define LL long long
 typedef pair<int,int> pii;
 const int inf = 0x3f3f3f3f;
 const int N =41e5+;
 #define clc(a,b) memset(a,b,sizeof(a))
 const double eps = 1e-;
 const int MOD = 1e9+;
 void fre() {freopen("in.txt","r",stdin);}
 void freout() {freopen("out.txt","w",stdout);}
 inline int read() {int x=,f=;char ch=getchar();while(ch>''||ch<'') {if(ch=='-') f=-;ch=getchar();}while(ch>=''&&ch<='') {x=x*+ch-'';ch=getchar();}return x*f;}

 int head[N],low[N],dfn[N],s[N];
 int cnt,tot;
 struct Edge{
     int v,w,nt;
     Edge(){}
     Edge(int v_,int w_,int nt_):v(v_),w(w_),nt(nt_){}
 }e[N<<];

 void add(int u,int v,int w){
     e[cnt]=Edge(v,w,head[u]);
     head[u]=cnt++;
 }
 pii mat[N];
 int rt;
 int ans;
 void tarjan(int u,int f){
     low[u] = dfn[u] = ++ tot;
     s[++s[]] = u;
     for(int i = head[u]; i != -; i = e[i].nt) {
         int v = e[i].v;
         if(v == f) continue;
         if(!dfn[v]) {
             mat[e[i].w] = make_pair(v, u);
             tarjan(v, u);
             low[u] = min(low[u], low[v]);
         }
         else {
             mat[e[i].w] = make_pair(u, v);
             low[u] = min(low[u], dfn[v]);
         }
     }
     if(dfn[u] == low[u]) {
         int res = ;
         while(s[s[]] != u) {
             ++ res;
             -- s[];
         }
         -- s[];
         if(ans < res) {ans = res; rt = u;}
     }
 }

 void init(){
     clc(head,-);
     tot=;
     cnt=;
     ans=;
 }
 int main(){
     init();
     int n,m;
     scanf("%d%d",&n,&m);
     for(int i=;i<=m;i++){
         int u,v;
         scanf("%d%d",&u,&v);
         add(u,v,i);
         add(v,u,i);
     }
     s[]=;
     tarjan(,-);
     clc(dfn,);
     tot=;
     s[]=;
     tarjan(rt,-);
     printf("%d\n",ans);
     for(int i=;i<=m;i++){
         printf("%d %d\n",mat[i].first,mat[i].second);
     }
     return ;
 }