#include <iostream>
#include <set>
#include <map>

int main() {
    std::map<int, int> linComp;
    std::map<int, int> colComp;
    std::map<int, int> compSiz;
    std::map<int, std::set<int>> compLin;
    std::map<int, std::set<int>> compCol;
    int nextComp = 1;
    int headCnt;
    std::cin >> headCnt;

    for (int i = 0; i < headCnt; ++i) {
        int line, col;
        std::cin >> line >> col;
        int firstComp = 0, secondComp = 0;
        if (linComp.count(line))
            firstComp = linComp[line];
        if (colComp.count(col))
            secondComp = colComp[col];

        if (!firstComp && !secondComp) {
            linComp[line] = nextComp;
            colComp[col] = nextComp;
            compSiz[nextComp] = 1;
            compLin[nextComp] = {line};
            compCol[nextComp] = {col};
            ++nextComp;
        }
        else if (!firstComp && secondComp) {
            linComp[line] = secondComp;
            ++compSiz[secondComp];
            compLin[secondComp].insert(line);
        }
        else if (firstComp && !secondComp) {
            colComp[col] = firstComp;
            ++compSiz[firstComp];
            compCol[firstComp].insert(col);
        }
        else if (firstComp == secondComp) {
            ++compSiz[firstComp];
        }
        else {
            int bigger, smaller;
            if (compSiz[firstComp] > compSiz[secondComp]) {
                bigger = firstComp;
                smaller = secondComp;
            }
            else {
                bigger = secondComp;
                smaller = firstComp;
            }
            compSiz[bigger] += compSiz[smaller] + 1;
            for (int l : compLin[smaller]) {
                linComp[l] = bigger;
                compLin[bigger].insert(l);
            }
            for (int c : compCol[smaller]) {
                colComp[c] = bigger;
                compCol[bigger].insert(c);
            }
            compSiz.erase(smaller);
            compLin.erase(smaller);
            compCol.erase(smaller);
        }
    }
    std::cout << compSiz.size() - 1 << std::endl;
    return 0;
}