题解 | 诗

package main

import (
	"bufio"
	"fmt"
	"os"
	"strings"
)

func main() {
    reader := bufio.NewReader(os.Stdin)
    s, _ := reader.ReadString('\n')
    part := strings.Split(strings.TrimSpace(s), "")
	index := 0
    n:=len(part)
	for i := 0; index+i < n; i++ {
		index += i
        fmt.Print(part[index])
	}

}