题解 | #DNA序列#

let str = readline()
let num = readline()
let result = ''
let max = 0
for(let i = 0; i <= (str.length - num); i++) {
    let s = str.substr(i, num).split('').filter(item => item == 'C' || item == 'G').length
    if (s > max) {
        result = str.substr(i, num)
        max = s
    }
}
console.log(result)