"use strict"

const main = (input) => {
    input = input.split("");
    const S = new Set(input);
    let sum1 = 0;
    let sum2 = 0;

    for (let i = 0; i < input.length; i++){
        if (input[0] == input[i]) {
            sum1 += 1;
        } else {
            sum2 += 1;
        }
    }

    if (S.size == 2 && sum1 == 2 && sum2 == 2) {
        console.log("Yes");
    } else {
        console.log("No");
    }
};

main(require("fs").readFileSync("/dev/stdin", "utf8"));