#include <bits/stdc++.h>
using namespace std;
using ll=long long;
using ull=unsigned long long;
using P=pair<ll,ll>;
template<typename T>using minque=priority_queue<T,vector<T>,greater<T>>;
template<typename T>bool chmax(T &a,const T &b){return (a<b?(a=b,true):false);}
template<typename T>bool chmin(T &a,const T &b){return (a>b?(a=b,true):false);}
template<typename T1,typename T2>istream &operator>>(istream &is,pair<T1,T2>&p){is>>p.first>>p.second;return is;}
template<typename T1,typename T2,typename T3>istream &operator>>(istream &is,tuple<T1,T2,T3>&a){is>>std::get<0>(a)>>std::get<1>(a)>>std::get<2>(a);return is;}
template<typename T,size_t n>istream &operator>>(istream &is,array<T,n>&a){for(auto&i:a)is>>i;return is;}
template<typename T>istream &operator>>(istream &is,vector<T> &a){for(auto &i:a)is>>i;return is;}
template<typename T1,typename T2>void operator++(pair<T1,T2>&a,int n){a.first++,a.second++;}
template<typename T1,typename T2>void operator--(pair<T1,T2>&a,int n){a.first--,a.second--;}
template<typename T>void operator++(vector<T>&a,int n){for(auto &i:a)i++;}
template<typename T>void operator--(vector<T>&a,int n){for(auto &i:a)i--;}
#define overload3(_1,_2,_3,name,...) name
#define rep1(i,n) for(int i=0;i<(int)(n);i++)
#define rep2(i,l,r) for(int i=(int)(l);i<(int)(r);i++)
#define rep(...) overload3(__VA_ARGS__,rep2,rep1)(__VA_ARGS__)
#define reps(i,l,r) rep2(i,l,r)
#define all(x) x.begin(),x.end()
#define pcnt(x) __builtin_popcountll(x)
#define fin(x) return cout<<(x)<<'\n',static_cast<void>(0)
#define yn(x) cout<<((x)?"Yes\n":"No\n")
#define uniq(x) sort(all(x)),x.erase(unique(all(x)),x.end())
template<typename T>
inline int fkey(vector<T>&z,T key){return lower_bound(z.begin(),z.end(),key)-z.begin();}
ll myceil(ll a,ll b){return (a+b-1)/b;}
template<typename T,size_t n,size_t id=0>
auto vec(const int (&d)[n],const T &init=T()){
  if constexpr (id<n)return vector(d[id],vec<T,n,id+1>(d,init));
  else return init;
}
#ifdef LOCAL
#include<debug.h>
#define SWITCH(a,b) (a)
#else
#define debug(...) static_cast<void>(0)
#define debugg(...) static_cast<void>(0)
#define SWITCH(a,b) (b)
template<typename T1,typename T2>ostream &operator<<(ostream &os,const pair<T1,T2>&p){os<<p.first<<' '<<p.second;return os;}
#endif
struct Timer{
  clock_t start;
  Timer(){
    start=clock();
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout<<fixed<<setprecision(16);
  }
  inline double now(){return (double)(clock()-start)/1000;}
  #ifdef LOCAL
  ~Timer(){
    cerr<<"time:";
    cerr<<now();
    cerr<<"ms\n";
  }
  #endif
}timer;
void SOLVE();
int main(){
  int testcase=1;
  //cin>>testcase;
  for(int i=0;i<testcase;i++){
    SOLVE();
  }
}
template<typename T=int>
struct Edge{
  int from,to;
  T weight;
  int index;
  Edge(int from_,int to_,T weight_=T(),int index_=-1):from(from_),to(to_),weight(weight_),index(index_){}
  Edge():from(-1),to(-1),weight(),index(-1){}
  friend std::ostream &operator<<(std::ostream &os,const Edge&e){
    os<<'[';
    os<<"from:"<<e.from;
    os<<"to:"<<e.to;
    os<<"weight:"<<e.weight;
    os<<"index:"<<e.index;
    os<<']';
    return os;
  }
};
template<typename T=int>
struct Graph{
private:
  int n;
  std::vector<Edge<T>>edge;
  std::vector<Edge<T>>g;
  std::vector<int>ptr;
  bool directed;
  struct graph_range{
    using iterator=typename std::vector<Edge<T>>::iterator;
    iterator l,r;
    iterator begin()const{return l;}
    iterator end()const{return r;}
    int size()const{return r-l;}
    Edge<T> &operator[](int i)const{return l[i];}
  };
  struct const_graph_range{
    using iterator=typename std::vector<Edge<T>>::const_iterator;
    iterator l,r;
    iterator begin()const{return l;}
    iterator end()const{return r;}
    int size()const{return r-l;}
    const Edge<T> &operator[](int i)const{return l[i];}
  };
public:
  Graph(int n_,bool dir_):n(n_),directed(dir_){}
  Graph():n(0){}
  Graph(int n_,bool dir_,const std::vector<Edge<T>>&e):n(n_),directed(dir_),edge(e){build();}
  template<bool weighted=false,bool index=1>
  void read(int m){
    edge.reserve(m);
    for(int i=0;i<m;i++){
      int u,v;
      std::cin>>u>>v;
      T w;
      if constexpr(index)u--,v--;
      if constexpr(weighted)std::cin>>w;
      else w=1;
      edge.emplace_back(u,v,w,i);
    }
    build();
  }
  void add_edge(int u,int v){
    assert(0<=u&&u<n);
    assert(0<=v&&v<n);
    int id=edge.size();
    edge.emplace_back(u,v,1,id);
  }
  void add_edge(int u,int v,T w){
    assert(0<=u&&u<n);
    assert(0<=v&&v<n);
    int id=edge.size();
    edge.emplace_back(u,v,w,id);
  }
  void add_edge(int u,int v,T w,int index){
    assert(0<=u&&u<n);
    assert(0<=v&&v<n);
    edge.emplace_back(u,v,w,index);
  }
  void add_edge(Edge<T>e){
    edge.emplace_back(e);
  }
  void build(){
    std::vector<int>cnt(n+1,0);
    for(const Edge<T>&e:edge){
      cnt[e.from+1]++;
      if(!directed)cnt[e.to+1]++;
    }
    for(int i=1;i<=n;i++)cnt[i]+=cnt[i-1];
    ptr=cnt;
    g.resize(cnt[n]);
    for(const Edge<T>&e:edge){
      g[cnt[e.from]++]=e;
      if(!directed)g[cnt[e.to]++]=Edge<T>(e.to,e.from,e.weight,e.index);
    }
  }
  void reverse(){
    if(directed){
      for(Edge<T>&e:edge)std::swap(e.from,e.to);
      build();
    }
  }
  inline void to_directed(){
    directed=true;
    build();
  }
  inline void to_undirected(){
    directed=false;
    build();
  }
  void reserve(int m){edge.reserve(m);}
  graph_range operator[](int i){return graph_range{g.begin()+ptr[i],g.begin()+ptr[i+1]};}
  const_graph_range operator[](int i)const{return const_graph_range{g.begin()+ptr[i],g.begin()+ptr[i+1]};}
  const Edge<T>& get_edge(int i)const{return edge[i];}
  std::vector<Edge<T>>get_edges()const{return edge;}
  inline bool is_directed()const{return directed;}
  inline int size()const{return n;}
  inline int edge_size()const{return edge.size();}
  typename std::vector<Edge<T>>::iterator begin(){return edge.begin();}
  typename std::vector<Edge<T>>::iterator end(){return edge.end();}
  typename std::vector<Edge<T>>::const_iterator begin()const{return edge.begin();}
  typename std::vector<Edge<T>>::const_iterator end()const{return edge.end();}
};
//min
template<typename T>
struct Top2{
  int key1,key2;
  T top1,top2;
  Top2():key1(std::numeric_limits<int>::min()),key2(std::numeric_limits<int>::min()),top1(std::numeric_limits<T>::max()),top2(std::numeric_limits<T>::max()){}
  bool set(int k,T v){
    if(k==key1){
      if(top1>v){
        top1=v;
        return true;
      }
    }
    else if(top1>v){
      key2=key1;
      top2=top1;
      key1=k;
      top1=v;
      return true;
    }
    else if(top2>v){
      key2=k;
      top2=v;
      return true;
    }
    return false;
  }
  T neq_min(int k)const{return k!=key1?top1:top2;}
  bool contains(int k,T v)const{return (k==key1&&v==top1)||(k==key2&&v==top2);}
};
void SOLVE(){
  int n,m;
  cin>>n>>m;
  Graph<ll>g(n,true);
  g.read<1,1>(m);
  string s;
  cin>>s;
  string t="KCPC";
  vector<vector<Top2<ll>>>dst(5,vector<Top2<ll>>(n));
  minque<tuple<ll,int,int,int>>que;
  auto yaru=[&](int i,int j,int c,ll d)->void {
    if(dst[i][j].set(c,d)){
      que.emplace(d,c,i,j);
    }
  };
  yaru(0,0,-1,0);
  while(!que.empty()){
    auto [d,c,i,j]=que.top();que.pop();
    if(i==5)break;
    if(!dst[i][j].contains(c,d))continue;
    if(s[j]==t[i]){
      if(i==2)yaru(i+1,j,j,d);
      else if(c!=j)yaru(i+1,j,c,d);
    }
    for(auto e:g[j])yaru(i,e.to,c,d+e.weight);
  }
  ll ans=1e18;
  rep(i,n)chmin(ans,dst[4][i].top1);
  if(ans==1e18)ans=-1;
  cout<<ans<<endl;
}