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#include <cstdio>
#include <iostream>
#include <algorithm>
#include <string>
#include <vector>
#include <queue>
#include <string.h>

/* PA-2015 R3 */
/* Brute force, please do not expect too much :) */
using namespace std;

typedef vector<int> VI;
typedef long long LL;

#define FOR(x, b, e) for(int x = b; x <= (e); ++x)
#define FORD(x, b, e) for(int x = b; x >= (e); --x)
#define REP(x, n) for(int x = 0; x < (n); ++x)
#define VAR(v, n) __typeof(n) v = (n)
#define ALL(c) (c).begin(), (c).end()
#define SIZE(x) ((int)(x).size())
#define FOREACH(i, c) for(VAR(i, (c).begin()); i != (c).end(); ++i)
#define PB push_back
#define ST first
#define ND second

int na [1000100];
int orig [1000100];
char inp [1000100];

int mx_desc [1000100];

int nwdf(int a, int b)
{
	while(b) swap(a %= b, b);
	return a;
}

int main()
{
	int n, k;
	scanf("%d", &n);
	REP(i, n)
	{
		scanf("%d", &(na[i]));
		orig[i] = na[i];
	}
	scanf("%d", &k);
	int read = 0;

	scanf("%s", inp);

	int nwd = nwdf(k, n);

	if(strstr(inp, "P") == NULL)
	{
		printf("%d\n", -1);
		return 0;	
	}
	

	int cnt = 0;
	while(1)
	{
		na[cnt % n] += inp[cnt % k] == 'W' ? 1 : -1;
		if(na[cnt % n ] == 0)
		{
			goto exit;
		}
		cnt++;

		if (cnt == k * n / nwd)
		{
			bool impr = false;
			REP(i, n)
			{
				if(na[i] < orig[i])
				{
					impr = true;
					break;
				}
			}

			if(!impr)
			{
				printf("%d\n", -1);
				return 0;	
			}
		}
		if(cnt == 200000000)
		{
			printf("%d\n", -1);
			return 0;
		}
	}

exit:
	printf("%d\n", cnt + 1);	

	return 0;
}