#include <iostream>
using namespace std;

int main() {
    int n;
    cout << "Enter a four-digit number: ";
    cin >> n;

    if (n < 1000 || n > 9999) {
        cout << "Error! This is not a four-digit number." << endl;
    } else {
        int a = n / 1000;
        int b = (n / 100) % 10;
        int c = (n / 10) % 10;
        int d = n % 10;
        int r = c * 1000 + d * 100 + a * 10 + b;
        cout << "Result: " << r << endl;
    }
    return 0;
}