278.cpp

#include <iostream>
#include <cmath>
#include <cstdio>

using namespace std;

double getS(double ax, double ay, double bx, double by);

int main(){

    double cx, cy, ax, ay, bx, by;
    cin >> cx >> cy >> ax >> ay >> bx >> by;
    bx -= ax;
    cx -= ax;
    by -= ay;
    cy -= ay;

    if (bx * cx + by * cy >= 0)
        cout << abs(getS(bx, by, cx, cy)) / sqrt(bx * bx + by * by);
    else
        cout << sqrt(cx * cx + cy * cy) << endl;

    return 0;
}

double getS(double ax, double ay, double bx, double by){
    return (bx * ay - ax * by);
}