package main import ( "bufio" "errors" "fmt" "io" "math" "os" "strconv" ) /********** I/O usage **********/ //str := ReadString() //i := ReadInt() //X := ReadIntSlice(n) //S := ReadRuneSlice() //a := ReadFloat64() //A := ReadFloat64Slice(n) //str := ZeroPaddingRuneSlice(num, 32) //str := PrintIntsLine(X...) /*******************************************************************/ const MOD = 1000000000 + 7 const ALPHABET_NUM = 26 const INF_INT64 = math.MaxInt64 const INF_BIT60 = 1 << 60 var n int func main() { n = ReadInt() if n == 1 { fmt.Println(0) return } if n == 2 { fmt.Println(1) return } ans := 1 for r := 3; r <= n; r += 2 { if r*r > 2*n { break } if !IsPrime(r) { continue } num := r*r - 2 if IsPrime(num) && num <= n { ans += 2 } } fmt.Println(ans) } // IsPrime judges whether an argument integer is a prime number or not. func IsPrime(n int) bool { if n == 1 { return false } for i := 2; i*i <= n; i++ { if n%i == 0 { return false } } return true } // MODはとったか? // 遷移だけじゃなくて最後の最後でちゃんと取れよ? /*******************************************************************/ /*********** I/O ***********/ var ( // ReadString returns a WORD string. ReadString func() string stdout *bufio.Writer ) func init() { ReadString = newReadString(os.Stdin) stdout = bufio.NewWriter(os.Stdout) } func newReadString(ior io.Reader) func() string { r := bufio.NewScanner(ior) r.Buffer(make([]byte, 1024), int(1e+11)) // Split sets the split function for the Scanner. The default split function is ScanLines. // Split panics if it is called after scanning has started. r.Split(bufio.ScanWords) return func() string { if !r.Scan() { panic("Scan failed") } return r.Text() } } // ReadInt returns an integer. func ReadInt() int { return int(readInt64()) } func readInt64() int64 { i, err := strconv.ParseInt(ReadString(), 0, 64) if err != nil { panic(err.Error()) } return i } // ReadIntSlice returns an integer slice that has n integers. func ReadIntSlice(n int) []int { b := make([]int, n) for i := 0; i < n; i++ { b[i] = ReadInt() } return b } // ReadFloat64 returns an float64. func ReadFloat64() float64 { return float64(readFloat64()) } func readFloat64() float64 { f, err := strconv.ParseFloat(ReadString(), 64) if err != nil { panic(err.Error()) } return f } // ReadFloatSlice returns an float64 slice that has n float64. func ReadFloat64Slice(n int) []float64 { b := make([]float64, n) for i := 0; i < n; i++ { b[i] = ReadFloat64() } return b } // ReadRuneSlice returns a rune slice. func ReadRuneSlice() []rune { return []rune(ReadString()) } /*********** Debugging ***********/ // ZeroPaddingRuneSlice returns binary expressions of integer n with zero padding. // For debugging use. func ZeroPaddingRuneSlice(n, digitsNum int) []rune { sn := fmt.Sprintf("%b", n) residualLength := digitsNum - len(sn) if residualLength <= 0 { return []rune(sn) } zeros := make([]rune, residualLength) for i := 0; i < len(zeros); i++ { zeros[i] = '0' } res := []rune{} res = append(res, zeros...) res = append(res, []rune(sn)...) return res } /*********** DP sub-functions ***********/ // ChMin accepts a pointer of integer and a target value. // If target value is SMALLER than the first argument, // then the first argument will be updated by the second argument. func ChMin(updatedValue *int, target int) bool { if *updatedValue > target { *updatedValue = target return true } return false } // ChMax accepts a pointer of integer and a target value. // If target value is LARGER than the first argument, // then the first argument will be updated by the second argument. func ChMax(updatedValue *int, target int) bool { if *updatedValue < target { *updatedValue = target return true } return false } // NthBit returns nth bit value of an argument. // n starts from 0. func NthBit(num, nth int) int { return num >> uint(nth) & 1 } // OnBit returns the integer that has nth ON bit. // If an argument has nth ON bit, OnBit returns the argument. func OnBit(num, nth int) int { return num | (1 << uint(nth)) } // OffBit returns the integer that has nth OFF bit. // If an argument has nth OFF bit, OffBit returns the argument. func OffBit(num, nth int) int { return num & ^(1 << uint(nth)) } // PopCount returns the number of ON bit of an argument. func PopCount(num int) int { res := 0 for i := 0; i < 70; i++ { if ((num >> uint(i)) & 1) == 1 { res++ } } return res } /*********** Arithmetic ***********/ // Max returns the max integer among input set. // This function needs at least 1 argument (no argument causes panic). func Max(integers ...int) int { m := integers[0] for i, integer := range integers { if i == 0 { continue } if m < integer { m = integer } } return m } // Min returns the min integer among input set. // This function needs at least 1 argument (no argument causes panic). func Min(integers ...int) int { m := integers[0] for i, integer := range integers { if i == 0 { continue } if m > integer { m = integer } } return m } // DigitSum returns digit sum of a decimal number. // DigitSum only accept a positive integer. func DigitSum(n int) int { if n < 0 { return -1 } res := 0 for n > 0 { res += n % 10 n /= 10 } return res } // Sum returns multiple integers sum. func Sum(integers ...int) int { s := 0 for _, i := range integers { s += i } return s } // CeilInt returns the minimum integer larger than or equal to float(a/b). func CeilInt(a, b int) int { res := a / b if a%b > 0 { res++ } return res } // FloorInt returns the maximum integer smaller than or equal to float(a/b) func FloorInt(a, b int) int { res := a / b return res } // PowInt is integer version of math.Pow // PowInt calculate a power by Binary Power (二分累乗法(O(log e))). func PowInt(a, e int) int { if a < 0 || e < 0 { panic(errors.New("[argument error]: PowInt does not accept negative integers")) } if e == 0 { return 1 } if e%2 == 0 { halfE := e / 2 half := PowInt(a, halfE) return half * half } return a * PowInt(a, e-1) } // AbsInt is integer version of math.Abs func AbsInt(a int) int { if a < 0 { return -a } return a } // Gcd returns the Greatest Common Divisor of two natural numbers. // Gcd only accepts two natural numbers (a, b >= 1). // 0 or negative number causes panic. // Gcd uses the Euclidean Algorithm. func Gcd(a, b int) int { if a <= 0 || b <= 0 { panic(errors.New("[argument error]: Gcd only accepts two NATURAL numbers")) } if a < b { a, b = b, a } // Euclidean Algorithm for b > 0 { div := a % b a, b = b, div } return a } // Lcm returns the Least Common Multiple of two natural numbers. // Lcd only accepts two natural numbers (a, b >= 1). // 0 or negative number causes panic. // Lcd uses the Euclidean Algorithm indirectly. func Lcm(a, b int) int { if a <= 0 || b <= 0 { panic(errors.New("[argument error]: Gcd only accepts two NATURAL numbers")) } // a = a'*gcd, b = b'*gcd, a*b = a'*b'*gcd^2 // a' and b' are relatively prime numbers // gcd consists of prime numbers, that are included in a and b gcd := Gcd(a, b) // not (a * b / gcd), because of reducing a probability of overflow return (a / gcd) * b } // Strtoi is a wrapper of `strconv.Atoi()`. // If `strconv.Atoi()` returns an error, Strtoi calls panic. func Strtoi(s string) int { if i, err := strconv.Atoi(s); err != nil { panic(errors.New("[argument error]: Strtoi only accepts integer string")) } else { return i } } // PrintIntsLine returns integers string delimited by a space. func PrintIntsLine(A ...int) string { res := []rune{} for i := 0; i < len(A); i++ { str := strconv.Itoa(A[i]) res = append(res, []rune(str)...) if i != len(A)-1 { res = append(res, ' ') } } return string(res) }