题解 | #统计每个月兔子的总数#

const rl = require("readline").createInterface({ input: process.stdin });

rl.on('line',line => {
    let n = parseInt(line)
    let month = 1
    //刚出生
    let a = 1
    //待成熟
    let b = 0
    //可生育
    let c = 0
    while(++month <= n) {
        c += b
        b = a
        a = c
    }
    console.log(a+b+c)
})