#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#pragma GCC optimize("inline")
#include<bits/stdc++.h>
using namespace std;
void*wmem;
char memarr[96000000];
template<class T> inline void walloc1d(T **arr, int x, void **mem = &wmem){
  static int skip[16] = {0, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1};
  (*mem) = (void*)( ((char*)(*mem)) + skip[((unsigned long long)(*mem)) & 15] );
  (*arr)=(T*)(*mem);
  (*mem)=((*arr)+x);
}
template<class T> inline void walloc1d(T **arr, int x1, int x2, void **mem = &wmem){
  walloc1d(arr, x2-x1, mem);
  (*arr) -= x1;
}
inline int my_getchar_unlocked(){
  static char buf[1048576];
  static int s = 1048576;
  static int e = 1048576;
  if(s == e && e == 1048576){
    e = fread_unlocked(buf, 1, 1048576, stdin);
    s = 0;
  }
  if(s == e){
    return EOF;
  }
  return buf[s++];
}
inline void rd(int &x){
  int k;
  int m=0;
  x=0;
  for(;;){
    k = my_getchar_unlocked();
    if(k=='-'){
      m=1;
      break;
    }
    if('0'<=k&&k<='9'){
      x=k-'0';
      break;
    }
  }
  for(;;){
    k = my_getchar_unlocked();
    if(k<'0'||k>'9'){
      break;
    }
    x=x*10+k-'0';
  }
  if(m){
    x=-x;
  }
}
struct MY_WRITER{
  char buf[1048576];
  int s;
  int e;
  MY_WRITER(){
    s = 0;
    e = 1048576;
  }
  ~MY_WRITER(){
    if(s){
      fwrite_unlocked(buf, 1, s, stdout);
    }
  }
}
;
MY_WRITER MY_WRITER_VAR;
void my_putchar_unlocked(int a){
  if(MY_WRITER_VAR.s == MY_WRITER_VAR.e){
    fwrite_unlocked(MY_WRITER_VAR.buf, 1, MY_WRITER_VAR.s, stdout);
    MY_WRITER_VAR.s = 0;
  }
  MY_WRITER_VAR.buf[MY_WRITER_VAR.s++] = a;
}
inline void wt_L(char a){
  my_putchar_unlocked(a);
}
inline void wt_L(int x){
  int s=0;
  int m=0;
  char f[10];
  if(x<0){
    m=1;
    x=-x;
  }
  while(x){
    f[s++]=x%10;
    x/=10;
  }
  if(!s){
    f[s++]=0;
  }
  if(m){
    my_putchar_unlocked('-');
  }
  while(s--){
    my_putchar_unlocked(f[s]+'0');
  }
}
struct unionFind{
  int*d;
  int N;
  int M;
  inline void malloc(const int n){
    d = (int*)std::malloc(n*sizeof(int));
    M = n;
  }
  inline void malloc(const int n, const int fg){
    d = (int*)std::malloc(n*sizeof(int));
    M = n;
    if(fg){
      init(n);
    }
  }
  inline void free(void){
    std::free(d);
  }
  inline void walloc(const int n, void **mem=&wmem){
    walloc1d(&d, n, mem);
    M = n;
  }
  inline void walloc(const int n, const int fg, void **mem=&wmem){
    walloc1d(&d, n, mem);
    M = n;
    if(fg){
      init(n);
    }
  }
  inline void init(const int n){
    int i;
    N = n;
    for(i=(0);i<(n);i++){
      d[i] = -1;
    }
  }
  inline void init(void){
    init(M);
  }
  inline int get(int a){
    int t = a;
    int k;
    while(d[t]>=0){
      t=d[t];
    }
    while(d[a]>=0){
      k=d[a];
      d[a]=t;
      a=k;
    }
    return a;
  }
  inline int connect(int a, int b){
    if(d[a]>=0){
      a=get(a);
    }
    if(d[b]>=0){
      b=get(b);
    }
    if(a==b){
      return 0;
    }
    if(d[a] < d[b]){
      d[a] += d[b];
      d[b] = a;
    }
    else{
      d[b] += d[a];
      d[a] = b;
    }
    return 1;
  }
  inline int operator()(int a){
    return get(a);
  }
  inline int operator()(int a, int b){
    return connect(a,b);
  }
  inline int& operator[](const int a){
    return d[a];
  }
  inline int size(int a){
    a = get(a);
    return -d[a];
  }
  inline int sizeList(int res[]){
    int i;
    int sz=0;
    for(i=(0);i<(N);i++){
      if(d[i]<0){
        res[sz++] = -d[i];
      }
    }
    return sz;
  }
  inline int comp(int res[], void *mem = wmem){
    int i;
    int sz=0;
    int*cnt;
    walloc1d(&cnt, N, &mem);
    for(i=(0);i<(N);i++){
      cnt[i] = 0;
    }
    for(i=(0);i<(N);i++){
      cnt[get(i)] = 1;
    }
    for(i=(0);i<(N);i++){
      if(cnt[i]){
        cnt[i] = sz++;
      }
    }
    for(i=(0);i<(N);i++){
      res[i] = cnt[get(i)];
    }
    return sz;
  }
}
;
template<class T> int coordcomp_L(int n, T arr[], int res[] = NULL, void *mem = wmem){
  int i;
  int k = 0;
  pair<T,int>*r;
  walloc1d(&r, n, &mem);
  for(i=(0);i<(n);i++){
    r[i].first = arr[i];
    r[i].second = i;
  }
  sort(r, r+n);
  if(res != NULL){
    for(i=(0);i<(n);i++){
      if(i && r[i].first != r[i-1].first){
        k++;
      }
      res[r[i].second] = k;
    }
  }
  else{
    for(i=(0);i<(n);i++){
      if(i && r[i].first != r[i-1].first){
        k++;
      }
      arr[r[i].second] = k;
    }
  }
  return k+1;
}
template<class T> int coordcomp_L(int n1, T arr1[], int n2, T arr2[], int res1[] = NULL, int res2[] = NULL, void *mem = wmem){
  int i;
  int k = 0;
  pair<T,int>*r;
  walloc1d(&r, n1+n2, &mem);
  for(i=(0);i<(n1);i++){
    r[i].first = arr1[i];
    r[i].second = i;
  }
  for(i=(0);i<(n2);i++){
    r[n1+i].first = arr2[i];
    r[n1+i].second = n1+i;
  }
  sort(r, r+n1+n2);
  for(i=(0);i<(n1+n2);i++){
    if(i && r[i].first != r[i-1].first){
      k++;
    }
    if(r[i].second < n1){
      if(res1!=NULL){
        res1[r[i].second] = k;
      }
      else{
        arr1[r[i].second] = k;
      }
    }
    else{
      if(res2!=NULL){
        res2[r[i].second-n1] = k;
      }
      else{
        arr2[r[i].second-n1] = k;
      }
    }
  }
  return k+1;
}
int N;
int A[200000];
int B[200000];
unionFind uf;
int sz;
int chk;
int deg[200000];
int main(){
  int i;
  wmem = memarr;
  rd(N);
  {
    int Lj4PdHRW;
    for(Lj4PdHRW=(0);Lj4PdHRW<(N);Lj4PdHRW++){
      rd(A[Lj4PdHRW]);
      rd(B[Lj4PdHRW]);
    }
  }
  sz =coordcomp_L(N,A,N,B);
  uf.walloc(sz,1);
  for(i=(0);i<(N);i++){
    chk += uf(A[i], B[i]);
  }
  if(chk != sz-1){
    wt_L(0);
    wt_L('\n');
    return 0;
  }
  for(i=(0);i<(N);i++){
    deg[A[i]]++;
    deg[B[i]]--;
  }
  int xr20shxY;
  remove_reference<decltype(abs(deg[xr20shxY]))>::type WYIGIcGE;
  int t_ynMSdg = 0;
  if((0) > ((sz)-1)){
    WYIGIcGE = 0;
  }
  else{
    for(xr20shxY = 0; xr20shxY <= (sz)-1; xr20shxY++){
      if(t_ynMSdg == 0){
        WYIGIcGE = abs(deg[xr20shxY]);
        t_ynMSdg = 1;
        continue;
      }
      WYIGIcGE += abs(deg[xr20shxY]);
    }
    if(t_ynMSdg==0){
      WYIGIcGE = 0;
    }
  }
  chk =WYIGIcGE;
  if(chk==0){
    wt_L(sz);
    wt_L('\n');
  }
  else if(chk==2){
    wt_L(1);
    wt_L('\n');
  }
  else{
    wt_L(0);
    wt_L('\n');
  }
  return 0;
}
// cLay version 20210708-1

// --- original code ---
// int N, A[2d5], B[];
// unionFind uf;
// int sz, chk, deg[];
// {
//   rd(N,(A,B)(N));
//   sz = coordcomp(N,A,N,B);
//   uf.walloc(sz,1);
//   rep(i,N) chk += uf(A[i], B[i]);
//   if(chk != sz-1) wt(0), return 0;
//   rep(i,N) deg[A[i]]++, deg[B[i]]--;
//   chk = sum[i,0,sz](abs(deg[i]));
//   wt(if[chk==0, sz, chk==2, 1, 0]);
// }