参考答案：

#include<iostream>
#include<string>
using namespace std;
int main()
{
    int l, r;
    cin >> l >> r;
    string s;
    int sum = 0;
    for (int i = l; i <= r; ++i) s += to_string(i);

    for (int i = 0; i < s.length(); ++i) if (s[i] == '2') ++sum;

    cout << sum << '\n';
    return 0;
}