import java.io.BufferedReader
import java.io.PrintWriter
import java.lang.StrictMath.*
import kotlin.comparisons.compareBy

var out: PrintWriter = PrintWriter(System.out)  // これを使って出力すると早い
fun main(args: Array<String>) {
    try {
        val s = ReadLib.readString().toCharArray()
        if (s.count() == s.distinct().count()){
            out.println("yes")
        } else{
            out.println("no")
        }

    } finally {
        out.flush()   // 消さない
    }
}

/**
 * 読み取り
 */
class ReadLib {
    companion object {
        private var reader: BufferedReader = System.`in`.bufferedReader()

        fun reset() {
            reader = System.`in`.bufferedReader()
        }

        fun readInt(): Int {
            return Integer.parseInt(reader.readLine())
        }

        // Int
        fun readIntArray(delimiters: String = " "): IntArray {
            return reader
                .readLine()
                .split(delimiters)
                .map { s -> Integer.parseInt(s) }
                .toIntArray()
        }

        fun readNTimesInt(n: Int): IntArray {
            return (1..n).map { readInt() }.toIntArray()
        }

        fun readNTimesIntArray(n: Int): Array<IntArray> {
            return (1..n).map { readIntArray() }.toTypedArray()
        }

        // long
        // TODO 別の方法を考える
        fun readLong(): Long {
            return reader.readLine().toLong()
        }

        fun readLongArray(delimiters: String = " "): LongArray {
            return reader.readLine()
                .split(delimiters)
                .map { s -> s.toLong() }
                .toLongArray()
        }

        fun readNTimesLong(n: Int): LongArray {
            return (1..n).map { readLong() }.toLongArray()
        }

        fun readString(): String {
            return reader.readLine()
        }

        fun readStringArray(delimiters: String = " "): Array<String> {
            return readString().split(delimiters).toTypedArray()
        }

        fun readNTimesCharArray(n: Int): Array<CharArray> {
            return (1..n).map { readString().toCharArray() }.toTypedArray()
        }

        fun readNTimesString(n: Int): Array<String> {
            return (1..n).map { readString() }.toTypedArray()
        }

    }
}

/**
 * 要素とその個数を出力
 */
fun <T> Array<T>.ofCountMap(): Map<T, Int> {
    return this.groupBy { it }.mapValues { it.value.count() }
}

/**
 * 文字とその個数を出力
 */
fun String.ofCountMap(): Map<Char, Int> {
    return this.toCharArray().ofCountMap()
}

/**
 * 文字とその個数を出力
 */
fun CharArray.ofCountMap(): Map<Char, Int> {
    return this.groupBy { it }.mapValues { it.value.count() }
}

/**
 * Combination, nCk mod p を求める
 * https://ja.wikipedia.org/wiki/%E3%83%A2%E3%82%B8%E3%83%A5%E3%83%A9%E9%80%86%E6%95%B0
 * http://drken1215.hatenablog.com/entry/2018/06/08/210000
 * @param maxN 最大のn
 * @param mod 素数p
 */
class ModCombination(private val maxN: Int, private val mod: Int = 1000000007) {
    private val fac: IntArray = IntArray(maxN)
    private val finv: IntArray = IntArray(maxN)

    init {
        val inv: IntArray = IntArray(maxN)
        fac[0] = 1
        fac[1] = 1

        inv[0] = 1
        inv[1] = 1
        for (i in 2..maxN) {
            fac[i] = fac[i - 1] * i % mod   // 累積
            // mod % i < i
            inv[i] = mod - ((inv[mod % i].toLong()) * (mod / i) % mod).toInt()
            finv[i] = finv[i - 1] * inv[i] % mod
        }
    }

    /**
     * nCk mod p
     */
    fun Calc(n: Int, k: Int): Int {
        if (n < k || n < 0 || k < 0) {
            return 0
        }

        return ((fac[n].toLong() * finv[k] % mod) * finv[n - k] % mod).toInt()
    }
}

class MyMath {
    companion object {
        // 最大公約数
        fun gcd(m: Long, n: Long): Long {
            var M = m
            var N = n
            while (M % N > 0) {
                val pN = N
                N = M % N
                M = pN
            }

            return N
        }

        // 素因数分解（試し割り）
        // http://sucrose.hatenablog.com/entry/2014/10/10/235805
        fun primeFactorization(n: Long): Map<Long, Long> {
            val primes = enumeratePrime(ceil(sqrt(n.toDouble())).toInt())
                .map { it.toLong() }
                .toLongArray()
            primes.sort()

            val counter = mutableMapOf<Long, Long>()
            var cn = n
            for (p in primes) {
                if (cn < p) {
                    break
                }

                while (cn % p == 0L) {
                    counter[p] = counter.getOrElse(p, { 0 }) + 1
                    cn /= p
                }
            }

            if (cn > 1) {
                counter[cn] = 1
            }

            return counter
        }

        // Nまでの素数列挙
        fun enumeratePrime(n: Int): IntArray {
            val isPrime = BooleanArray(n + 1) { true }
            val primes = mutableListOf<Int>()
            for (i in 2..n) {
                if (!isPrime[i]) {
                    continue
                }

                primes.add(i)
                for (j in i..n step i) {
                    isPrime[i] = false
                }
            }

            return primes.toIntArray()
        }
    }
}

Measured memory_bytes: 31940