//https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8 より
macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
    ($($r:tt)*) => {
        let s = {
            use std::io::Read;
            let mut s = String::new();
            std::io::stdin().read_to_string(&mut s).unwrap();
            s
        };
        let mut iter = s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
}

macro_rules! input_inner {
    ($iter:expr) => {};
    ($iter:expr, ) => {};
    ($iter:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($iter, $t);
        input_inner!{$iter $($r)*}
    };
}

macro_rules! read_value {
    ($iter:expr, ( $($t:tt),* )) => {
        ( $(read_value!($iter, $t)),* )
    };
    ($iter:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($iter, $t)).collect::<Vec<_>>()
    };
    ($iter:expr, chars) => {
        read_value!($iter, String).chars().collect::<Vec<char>>()
    };
    ($iter:expr, usize1) => {
        read_value!($iter, usize) - 1
    };
    ($iter:expr, $t:ty) => {
        $iter.next().unwrap().parse::<$t>().expect("Parse error")
    };
}

//

use std::cmp::*;

#[derive(Clone, Copy, PartialEq)]
struct Cost(f64);

impl Eq for Cost {
}

impl PartialOrd for Cost {
    fn partial_cmp(&self, rhs: &Self) -> Option<Ordering> {
        self.0.partial_cmp(&rhs.0)
    }
}

impl Ord for Cost {
    fn cmp(&self, rhs: &Self) -> Ordering {
        self.partial_cmp(rhs).unwrap()
    }
}

fn run() {
    input! {
        n: usize,
        m: usize,
        s: usize1,
        t: usize1,
        p: [(f64, f64); n],
        e: [(usize1, usize1); m],
    }
    let mut g = vec![vec![]; n];
    for (a, b) in e {
        let dx = p[a].0 - p[b].0;
        let dy = p[a].1 - p[b].1;
        let d = (dx * dx + dy * dy).sqrt();
        g[a].push((b, d));
        g[b].push((a, d));
    }
    let mut dp = vec![std::f64::MAX; n];
    let mut h = std::collections::BinaryHeap::new();
    dp[s] = 0.0;
    h.push(Reverse((Cost(dp[s]), s)));
    while let Some(Reverse((Cost(d), v))) = h.pop() {
        if d > dp[v] {
            continue;
        }
        for &(u, w) in g[v].iter() {
            let d = d + w;
            if d < dp[u] {
                dp[u] = d;
                h.push(Reverse((Cost(d), u)));
            }
        }
    }
    println!("{:.5}", dp[t]);
}

fn main() {
    run();
}