import std.stdio, std.array, std.string, std.conv, std.algorithm;
import std.typecons, std.range, std.random, std.math, std.container;
import std.numeric, std.bigint, core.bitop;


void main() {
    auto N = readln.chomp.to!int;
    auto A = iota(N).map!(_ => readln.split.map!(to!int).array).array;

    auto X = new int[](2*10^^5+10);
    auto Y = new int[](2*10^^5+10);

    foreach (a; A) X[a[0]]++;
    foreach (a; A) Y[a[1]]++;

    int indeg = 0;
    int outdeg = 0;

    foreach (i; 0..2*10^^5+10) {
        auto diff = X[i] - Y[i];
        if (abs(diff) >= 2) {
            writeln(0);
            return;
        }

        if (diff == 1) {
            indeg += 1;
        } else if (diff == -1) {
            outdeg += 1;
        }
    }

    if (indeg == 1 && outdeg == 1) {
        writeln(1);
        return;
    }

    if (indeg == 0 && outdeg == 0) {
        auto uf = new UnionFind(N);
        int[int] dict_in;
        int[int] dict_out;
        foreach (i, a; A) {
            if (a[0] in dict_out) {
                uf.unite(i.to!int, dict_out[a[0]]);
            }
            if (a[1] in dict_in) {
                uf.unite(i.to!int, dict_in[a[1]]);
            }
            dict_in[a[0]] = i.to!int;
            dict_out[a[1]] = i.to!int;
        }

        if (uf.table[uf.find(0)] == -N) {
            writeln(dict_in.keys.length);
            return;
        }

        writeln(0);
        return;
    }

    writeln(0);
    return;


}

class UnionFind {
    import std.algorithm : swap;

    int n;
    int[] table;

    this(int n) {
        this.n = n;
        table = new int[](n);
        table[] = -1;
    }

    int find(int x) {
        return table[x] < 0 ? x : (table[x] = find(table[x]));
    }

    void unite(int x, int y) {
        x = find(x);
        y = find(y);
        if (x == y) return;
        if (table[x] > table[y]) swap(x, y);
        table[x] += table[y];
        table[y] = x;
    }

    bool same(int x, int y) {
        return find(x) == find(y);
    }
}