文件目录

#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;
int main()
{
    double xa, xb, ya, yb;
    cin >> xa >> ya >> xb >> yb;
    double zjb1 = xa - xb;
    double zjb2 = ya - yb;
    double ab = sqrt(zjb1 * zjb1 + zjb2 * zjb2);
    cout << fixed << setprecision(3) << ab;
    return 0;
}