#include <bits/stdc++.h>
#include <atcoder/modint.hpp>
using namespace std;

using i32 = int;
using i64 = long long;
using i128 = __int128_t;
using f64 = double;
using p2 = pair<i64, i64>;
using p3 = tuple<i64, i64, i64>;
using mint = atcoder::modint998244353;
constexpr i64 inf = 1e18;

void _main();
int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(18);
  _main();
}

void _main() {
  i64 n, m;
  cin >> n >> m;
  vector<vector<p2>> g(n), h(n);
  for (i64 i = 0; i < m; i++) {
    i64 u, v, c;
    cin >> u >> v >> c;
    u--, v--;
    g[u].push_back({v, c});
    h[v].push_back({u, c});
  }
  string s;
  cin >> s;
  vector<vector<p2>> dp1(n, {{inf, inf}, {inf + 1, inf + 1}});
  {
    priority_queue<p3, vector<p3>, greater<p3>> que;
    auto merge = [&](i64 i, p2 x) -> bool {
      if (dp1[i][0].first > x.first) {
        if (dp1[i][0].second != x.second) dp1[i] = {x, dp1[i][0]};
        else dp1[i] = {x, dp1[i][1]};
        return true;
      } else if (dp1[i][0].second != x.second && dp1[i][1].first > x.first) {
        dp1[i] = {dp1[i][0], x};
        return true;
      }
      return false;
    };
    for (i64 i = 0; i < n; i++) {
      if (s[i] == 'C') {
        que.push({0, i, i});
        merge(i, {0, i});
      }
    }
    while (!que.empty()) {
      auto [d, i, j] = que.top();
      que.pop();
      if (dp1[i][0] != (p2){d, j} && dp1[i][1] != (p2){d, j}) continue;
      for (auto [ni, c] : h[i]) {
        if (merge(ni, {d + c, j})) {
          que.push({d + c, ni, j});
        }
      }
    }
    for (i64 i = 0; i < n; i++) {
      if (s[i] != 'P') dp1[i] = {{inf, inf}, {inf + 1, inf + 1}};
    }
  }
  vector<i64> dp2(n, inf);
  {
    priority_queue<p3, vector<p3>, greater<p3>> que;
    auto merge = [&](i64 i, p2 x) -> bool {
      if (dp1[i][0].first > x.first) {
        if (dp1[i][0].second != x.second) dp1[i] = {x, dp1[i][0]};
        else dp1[i] = {x, dp1[i][1]};
        return true;
      } else if (dp1[i][0].second != x.second && dp1[i][1].first > x.first) {
        dp1[i] = {dp1[i][0], x};
        return true;
      }
      return false;
    };
    for (i64 i = 0; i < n; i++) {
      if (s[i] == 'P') {
        for (auto [x, j] : dp1[i]) {
          que.push({x, i, j});
        }
      }
    }
    while (!que.empty()) {
      auto [d, i, j] = que.top();
      que.pop();
      if (dp1[i][0] != (p2){d, j} && dp1[i][1] != (p2){d, j}) continue;
      for (auto [ni, c] : h[i]) {
        if (merge(ni, {d + c, j})) {
          que.push({d + c, ni, j});
        }
      }
    }
    for (i64 i = 0; i < n; i++) {
      if (s[i] == 'C') {
        dp2[i] = dp1[i][0].second != i ? dp1[i][0].first : dp1[i][1].first;
      } else dp2[i] = inf;
    }
  }
  {
    priority_queue<p2, vector<p2>, greater<p2>> que;
    for (i64 i = 0; i < n; i++) {
      if (s[i] == 'C') {
        que.push({dp2[i], i});
      }
    }
    while (!que.empty()) {
      auto [d, i] = que.top();
      que.pop();
      if (dp2[i] < d) continue;
      for (auto [ni, c] : h[i]) {
        if (dp2[ni] > d + c) {
          dp2[ni] = d + c;
          que.push({d + c, ni});
        }
      }
    }
    for (i64 i = 0; i < n; i++) {
      if (s[i] != 'K') dp2[i] = inf;
    }
  }
  {
    priority_queue<p2, vector<p2>, greater<p2>> que;
    for (i64 i = 0; i < n; i++) {
      if (s[i] == 'K') {
        que.push({dp2[i], i});
      }
    }
    while (!que.empty()) {
      auto [d, i] = que.top();
      que.pop();
      if (dp2[i] < d) continue;
      for (auto [ni, c] : h[i]) {
        if (dp2[ni] > d + c) {
          dp2[ni] = d + c;
          que.push({d + c, ni});
        }
      }
    }
  }
  cout << (dp2[0] >= inf ? -1 : dp2[0]) << "\n";
}