use std::{
    cmp::Reverse,
    collections::{BinaryHeap, HashMap},
};

use proconio::{
    input,
    marker::{Chars, Usize1},
};

fn main() {
    input! {
        n: usize, m: usize,
        edges: [(Usize1, Usize1, usize); m],
        s: Chars,
    }

    let mut graph = vec![vec![]; n];
    for &(u, v, w) in &edges {
        graph[u].push((v, w));
    }

    let mut dist = HashMap::new();
    let mut heap: BinaryHeap<(Reverse<usize>, usize, Vec<usize>)> = BinaryHeap::new();
    dist.insert((0, vec![]), 0);
    heap.push((Reverse(0), 0, vec![]));

    let kcpc = ['K', 'C', 'P', 'C'];

    while let Some((Reverse(d), current, history)) = heap.pop() {
        let i = history.len();
        if d != dist[&(current, history.clone())] {
            continue;
        }

        let target = kcpc[history.len()];
        if target == s[current] && !history.contains(&current) {
            if i == 3 {
                println!("{}", d);
                return;
            } else {
                let mut nhistory = history.clone();
                nhistory.push(current);
                if !dist.contains_key(&(current, nhistory.clone())) {
                    dist.insert((current, nhistory.clone()), d);
                    heap.push((Reverse(d), current, nhistory));
                }
            }
        }

        for &(next, w) in &graph[current] {
            if dist
                .get(&(next, history.clone()))
                .copied()
                .unwrap_or(!0usize)
                > d + w
            {
                dist.insert((next, history.clone()), d + w);
                heap.push((Reverse(d + w), next, history.clone()));
            }
        }
    }

    println!("-1");
}