package main import ( "bufio" "fmt" "os" "sort" "strconv" ) var sc = bufio.NewScanner(os.Stdin) var wr = bufio.NewWriter(os.Stdout) func out(x ...interface{}) { fmt.Fprintln(wr, x...) } func getI() int { sc.Scan() i, e := strconv.Atoi(sc.Text()) if e != nil { panic(e) } return i } func getF() float64 { sc.Scan() i, e := strconv.ParseFloat(sc.Text(), 64) if e != nil { panic(e) } return i } func getInts(N int) []int { ret := make([]int, N) for i := 0; i < N; i++ { ret[i] = getI() } return ret } func getS() string { sc.Scan() return sc.Text() } // min, max, asub, absなど基本関数 func max(a, b int) int { if a > b { return a } return b } func min(a, b int) int { if a < b { return a } return b } func asub(a, b int) int { if a > b { return a - b } return b - a } func abs(a int) int { if a >= 0 { return a } return -a } func lowerBound(a []int, x int) int { idx := sort.Search(len(a), func(i int) bool { return a[i] >= x }) return idx } func upperBound(a []int, x int) int { idx := sort.Search(len(a), func(i int) bool { return a[i] > x }) return idx } type pair struct { idx0, idx1 int r int } func main() { defer wr.Flush() sc.Split(bufio.ScanWords) sc.Buffer([]byte{}, 1000000) // this template is new version. // use getI(), getS(), getInts(), getF() N := getI() x := make([]int, N) y := make([]int, N) for i := 0; i < N; i++ { x[i], y[i] = getI(), getI() } b := make([]pair, 0) for i := 0; i < N; i++ { for j := i + 1; j < N; j++ { dx := x[i] - x[j] dy := y[i] - y[j] b = append(b, pair{i, j, dx*dx + dy*dy}) } } sort.Slice(b, func(i, j int) bool { return b[i].r < b[j].r }) m := make([]int, N) cnt := 0 // out(b) for i := 0; i < len(b); i++ { if b[i].idx0 == 0 && m[b[i].idx1] == 0 { cnt++ m[b[i].idx1] = 1 // out(b[i]) } else if m[b[i].idx0] == 0 && m[b[i].idx1] == 0 { m[b[i].idx0] = 1 m[b[i].idx1] = 1 } } out(cnt) }