// ---------- begin input macro ----------
// reference: https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8
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, bytes) => {
        read_value!($iter, String).bytes().collect::<Vec<u8>>()
    };
    ($iter:expr, usize1) => {
        read_value!($iter, usize) - 1
    };
    ($iter:expr, $t:ty) => {
        $iter.next().unwrap().parse::<$t>().expect("Parse error")
    };
}
// ---------- end input macro ----------

fn dfs(v: usize, p: usize, g: &[Vec<(usize, u64, usize)>], dp: &mut [u64], used: &mut [bool], ans: &mut u64) {
    for &(u, w, k) in g[v].iter() {
        if p == k || used[k] {
            continue;
        }
        used[k] = true;
        if dp[u] == std::u64::MAX {
            dp[u] = dp[v] + w;
            dfs(u, k, g, dp, used, ans);
        } else if dp[u] < dp[v] {
            *ans = (*ans).min(dp[v] + w - dp[u]);
        }
    }
}

fn run() {
    input! {
        t: usize,
        n: usize,
        m: usize,
        e: [(usize1, usize1, u64); m],
    }
    assert!(t == 0);
    let mut g = vec![vec![]; n];
    for (i, &(a, b, c)) in e.iter().enumerate() {
        g[a].push((b, c, i));
        if t == 0 {
            g[b].push((a, c, i));
        }
    }
    let mut ans = std::u64::MAX;
    for v in 0..n {
        let mut dp = vec![std::u64::MAX; n];
        let mut used = vec![false; m];
        dp[v] = 0;
        dfs(v, m, &g, &mut dp, &mut used, &mut ans);
    }
    if ans == std::u64::MAX {
        println!("-1");
    } else {
        println!("{}", ans);
    }
}

fn main() {
    run();
}