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

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 = vec![[!0usize; 4]; n];
    let mut heap: BinaryHeap<(Reverse<usize>, usize, Vec<usize>)> = BinaryHeap::new();
    dist[0][0] = 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][i] {
            continue;
        }

        let target = kcpc[history.len()];
        if target == s[current] && !history.contains(&current) {
            if i == 3 {
                println!("{}", dist[current][i]);
                return;
            } else if dist[current][i + 1] > dist[current][i] {
                let mut nhistory = history.clone();
                nhistory.push(current);
                dist[current][i + 1] = dist[current][i];
                heap.push((Reverse(d), current, nhistory));
            }
        }

        for &(next, w) in &graph[current] {
            if dist[next][i] > dist[current][i] + w {
                dist[next][i] = dist[current][i] + w;
                heap.push((Reverse(dist[next][i]), next, history.clone()));
            }
        }
    }

    println!("-1");
}