package main import ( "bufio" "os" "strconv" "fmt" ) func main() { sc := NewScanner() N := sc.NextInt() A := sc.NextIntArray() diff := A[1] - A[0] if diff < 0 { fmt.Println(-1) } else { for i := 1; i < N; i++ { B := sc.NextIntArray() if B[1] - B[0] != diff { fmt.Println(-1) return } } fmt.Println(diff) } } func mapToInt(arr []string) []int { ret := make([]int, len(arr)) for i := 0; i < len(arr); i++ { var err error ret[i], err = strconv.Atoi(arr[i]) if err != nil { panic(err) } } return ret } type Scanner struct { r *bufio.Reader buf []byte p int } func NewScanner() *Scanner { rdr := bufio.NewReaderSize(os.Stdin, 1000) return &Scanner{r:rdr} } func (s *Scanner) Next() string { s.pre() start := s.p for ; s.p < len(s.buf); s.p++ { if s.buf[s.p] == ' ' { break } } result := string(s.buf[start:s.p]) s.p++ return result } func (s *Scanner) NextLine() string { s.pre() start := s.p s.p = len(s.buf) return string(s.buf[start:]) } func (s *Scanner) NextInt() int { v, _ := strconv.Atoi(s.Next()) return v } func (s *Scanner) NextInt64() int64 { v, _ := strconv.ParseInt(s.Next(), 10, 64) return v } func (s *Scanner) NextIntArray() []int { s.pre() start := s.p result := []int{} for ; s.p < len(s.buf) + 1; s.p++ { if s.p == len(s.buf) || s.buf[s.p] == ' ' { v, _ := strconv.ParseInt(string(s.buf[start:s.p]), 10, 0) result = append(result, int(v)) start = s.p + 1 } } return result } func (s *Scanner) NextInt64Array() []int64 { s.pre() start := s.p result := []int64{} for ; s.p < len(s.buf) + 1; s.p++ { if s.p == len(s.buf) || s.buf[s.p] == ' ' { v, _ := strconv.ParseInt(string(s.buf[start:s.p]), 10, 64) result = append(result, v) start = s.p + 1 } } return result } func (s *Scanner) NextMap() map[int]bool { s.pre() start := s.p mp := map[int]bool{} for ; s.p < len(s.buf); s.p++ { if s.buf[s.p] == ' ' { v, _ := strconv.Atoi(string(s.buf[start:s.p])) mp[v] = true start = s.p + 1 } } v, _ := strconv.Atoi(string(s.buf[start:s.p])) mp[v] = true return mp } func (s *Scanner) pre() { if s.p >= len(s.buf) { s.readLine() s.p = 0 } } func (s *Scanner) readLine() { s.buf = make([]byte, 0) for { l, p, e := s.r.ReadLine() if e != nil { panic(e) } s.buf = append(s.buf, l...) if !p { break } } } //aのb乗をします O(log b) func pow(a int, b int) int { total := 1 tmp := a for b > 0 { if b % 2 == 1 { total *= tmp } b /= 2 tmp *= tmp } return total }