[Link] https://AtCoder.jp/contests/abc237/tasks/abc237_c
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import java.util.*;
import java.io.*;
public class Main {
static BufferedReader br;
static StringBuilder sb = new StringBuilder();
public static void main(String[] args) throws IOException {
br = new BufferedReader(new InputStreamReader(System.in));
String s = br.readLine();
int l = -1, r = s.length();
int rlen = 0, llen = 0;
for(int i = 0; i < s.length(); i++) {
if(s.charAt(i) != 'a') {
break;
} else l = i;
}
for(int i = s.length() - 1; i >= 0; i--) {
if(s.charAt(i) != 'a') {
break;
} else r = i;
}
if(r <= l) {
println("Yes");
return;
}
if(l > s.length() - 1 - r) {
println("No");
return;
}
l++;
r--;
while(l < r) {
if(s.charAt(l) != s.charAt(r)) {
println("No");
return;
}
l++;
r--;
}
println("Yes");
}
static int toi(String s) { return Integer.parseInt(s); }
static String[] getLine() throws IOException { return br.readLine().split(" "); }
static int[] getArr() throws IOException { return Arrays.stream(br.readLine().split(" ")).mapToInt(Integer::parseInt).toArray(); }
static <T> void print(T s) { System.out.print(s); }
static <T> void println(T s) { System.out.println(s); }
}