#include <bits/stdc++.h>
#include <random>
using namespace std; typedef unsigned long long _ulong; typedef long long int lint; typedef pair<lint, lint> plint; typedef pair<double long, double long> pld;
#define ALL(x) (x).begin(), (x).end()
#define SZ(x) ((lint)(x).size())
#define FOR(i, begin, end) for(lint i=(begin),i##_end_=(end);i<i##_end_;++i)
#define IFOR(i, begin, end) for(lint i=(end)-1,i##_begin_=(begin);i>=i##_begin_;--i)
#define REP(i, n) FOR(i,0,n)
#define IREP(i, n) IFOR(i,0,n)
#define endk '\n'
#define fi first
#define se second
struct fast_ios { fast_ios() { cin.tie(nullptr), ios::sync_with_stdio(false), cout << fixed << setprecision(20); }; } fast_ios_;
template<class T> auto add = [](T a, T b) -> T { return a + b; };
template<class T> auto f_max = [](T a, T b) -> T { return max(a, b); };
template<class T> auto f_min = [](T a, T b) -> T { return min(a, b); };
template<class T> using V = vector<T>;
using Vl = V<lint>; using VVl = V<Vl>;
template< typename T > ostream& operator<<(ostream& os, const vector< T >& v) {
	for (int i = 0; i < (int)v.size(); i++) os << v[i] << (i + 1 != v.size() ? " " : "");
	return os;
}
template< typename T >istream& operator>>(istream& is, vector< T >& v) {
	for (T& in : v) is >> in;
	return is;
}
template<class T> bool chmax(T& a, const T& b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> bool chmin(T& a, const T& b) { if (b < a) { a = b; return 1; } return 0; }
lint gcd(lint a, lint b) { if (b == 0) return a; else return gcd(b, a % b); }
lint ceil(lint a, lint b) { return (a + b - 1) / b; }
lint digit(lint a) { return (lint)log10(a); }
lint e_dist(plint a, plint b) { return abs(a.fi - b.fi) * abs(a.fi - b.fi) + abs(a.se - b.se) * abs(a.se - b.se); }
lint m_dist(plint a, plint b) { return abs(a.fi - b.fi) + abs(a.se - b.se); }
void Worshall_Floyd(VVl& g) { REP(k, SZ(g)) REP(i, SZ(g)) REP(j, SZ(g)) chmin(g[i][j], g[i][k] + g[k][j]); }
const lint MOD = 1e9 + 7, INF = LLONG_MAX;
lint dx[8] = { 1, 0, -1, 0, 1, -1, 1, -1 }, dy[8] = { 0, 1, 0, -1, -1, -1, 1, 1 };
bool YN(bool flag) { cout << (flag ? "YES" : "NO") << endk; return flag; } bool yn(bool flag) { cout << (flag ? "Yes" : "No") << endk; return flag; }
struct Edge {
	lint from, to;
	lint cost;
	Edge(lint u, lint v, lint c) {
		cost = c;
		from = u;
		to = v;
	}
	bool operator<(const Edge& e) const {
		return cost < e.cost;
	}
};
struct WeightedEdge {
	lint to;
	lint cost;
	WeightedEdge(lint v, lint c = 1) {
		to = v;
		cost = c;
	}
	bool operator<(const WeightedEdge& e) const {
		return cost < e.cost;
	}
};
using WeightedGraph = V<V<WeightedEdge>>;
typedef pair<plint, lint> tlint;
typedef pair<plint, plint> qlint;
typedef pair<string, lint> valstring;

lint N, M, K;
int main() {
	cin >> N >> M >> K;
	Vl arr(K);
	cin >> arr;
	long double initok = 1;
	lint cnt = 1;
	if (M == 1 && K == 1) {
		cout << -1 << endk;
		return 0;
	}
	REP(i, K - 1) {
		if (arr[i] + 1 == arr[i + 1]) cnt++;
		else cnt = 1;
		if (cnt >= M) {
			cout << -1 << endk;
			return 0;
		}
	}
	auto check = [&](long double e0) {
		V<long double> dp(N + M + 1, 0);
		REP(i, K) dp[arr[i]] = -1;
		long double sum = M;
		IREP(i, N) {
			if (dp[i + M + 1] == -1) {
				sum -= e0 + 1;
			}
			else sum -= (dp[i + M + 1] + 1);
			if (dp[i + 1] == -1) {
				sum += e0 + 1;
			}
			else sum += (dp[i + 1] + 1);
			if(dp[i] != -1) dp[i] = sum / M;
		}
		return dp[0] <= e0;
	};

	long double ok = INF, ng = -1;
	REP(_, 100) {
		long double mid = (ok + ng) / 2;
		if (check(mid)) ok = mid;
		else ng = mid;
	}
	cout << ok << endk;
}
#include <iostream>
#include <cstdio>
#include <string>
#include <algorithm>
#include <utility>
#include <cmath>
#include <vector>
#include <stack>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <tuple>
#include <numeric>
#include <functional>
using namespace std;
typedef long long ll;
typedef vector<ll> vl;
typedef vector<vector<ll>> vvl;
typedef pair<ll, ll> P;
#define rep(i, n) for(ll i = 0; i < n; i++)
#define exrep(i, a, b) for(ll i = a; i <= b; i++)
#define out(x) cout << x << endl
#define exout(x) printf("%.10f\n", x)
#define chmax(x, y) x = max(x, y)
#define chmin(x, y) x = min(x, y)
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define pb push_back
#define re0 return 0
const ll mod = 1000000007;
const ll INF = 1e16;

// 'R' = 0, 'P' = 1, 'S' = 2 と対応させる

ll f(ll x, ll y) {
    if(x == y) {
        return x;
    }
    if(x+y == 1) {
        return 1;
    }
    else if(x+y == 2) {
        return 0;
    } 
    else if(x+y == 3) {
        return 2;
    } 
}

int main() {
    ll n, k;
    string s;
    cin >> n >> k >> s;

    vl two(k);  // two[i] : 2^i(mod.n)
    two[0] = 1;
    rep(i, k-1) {
        two[i+1] = 2*two[i]%n;
    }

    vvl dp(k+1, vl(n));  // dp[i][j] : i回戦で、区間の左端がjのときの勝者の手
    rep(j, n) {
        rep(x, 3) {
            if(s[j] == "RPS"[x]) {
                dp[0][j] = x;
            }
        }
    }
    rep(i, k) {
        rep(j, n) {
            dp[i+1][j] = f(dp[i][j], dp[i][(j + two[i])%n]);
        }
    }

    out("RPS"[dp[k][0]]);
    re0;
}