For problem statement at 0-999/800-899/890-899/897/problemA.txt this is a correct solution, but verifier at 0-999/800-899/890-899/897/verifierA.go ends with All tests passed can you fix the verifier? package main

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

func main() {
	in := bufio.NewReader(os.Stdin)
	out := bufio.NewWriter(os.Stdout)
	defer out.Flush()

	var n, m int
	if _, err := fmt.Fscan(in, &n, &m); err != nil {
		return
	}
	var s string
	fmt.Fscan(in, &s)
	b := []byte(s)
	for i := 0; i < m; i++ {
		var l, r int
		var c1s, c2s string
		fmt.Fscan(in, &l, &r, &c1s, &c2s)
		c1 := c1s[0]
		c2 := c2s[0]
		for j := l - 1; j < r; j++ {
			if b[j] == c1 {
				b[j] = c2
			}
		}
	}
	fmt.Fprintln(out, string(b))
}