import { createInterface } from 'readline'


async function main() {
    const input = await new Promise(res => createInterface(process.stdin, process.stdout).once('line', res));
    const list = 'abcdefghijklmnopqrstuvwxyz'
    const i = list.findIndex((c, i) => c !== input[i])

    console.log(`${list[i]}to${input[i]}`)
}

main()