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735d.go
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735d.go
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// 00
package main
import (
"bufio"
"fmt"
"os"
)
func write(f *bufio.Writer, a ...interface{}) {
f.Write([]byte(fmt.Sprint(a...)))
}
type Number interface {
int64 | float64 | int
}
func min[K Number](a K, b K) K {
if a < b {
return a
}
return b
}
func max[K Number](a K, b K) K {
if a > b {
return a
}
return b
}
func bisect_right(a []int64, x int64) int {
lo := 0
hi := len(a)
for lo < hi {
mid := (lo + hi) / 2
if x < a[mid] {
hi = mid
} else {
lo = mid + 1
}
}
return lo
}
func is_prime(n int64, primes []int64) bool {
for i := 0; i < len(primes); i++ {
if primes[i]*primes[i] > n {
return true
}
if n%primes[i] == 0 {
return false
}
}
return true
}
func main() {
var n int64
reader := bufio.NewReader(os.Stdin)
f := bufio.NewWriter(os.Stdout)
defer f.Flush()
fmt.Fscan(reader, &n)
primes := make([]int64, 1)
primes[0] = 2
for start := int64(3); start*start <= n; start++ {
ok := true
for i := 0; i < len(primes); i++ {
if start%primes[i] == 0 {
ok = false
break
}
}
if ok {
primes = append(primes, start)
}
}
if n == 2 {
write(f, "1\n")
} else if n%2 == 0 {
write(f, "2\n")
} else if is_prime(n, primes) {
write(f, "1\n")
} else if is_prime(n-2, primes) {
write(f, "2\n")
} else {
write(f, "3\n")
}
}