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| #include<bits/stdc++.h>
#define ll long long
#define ull unsigned long long
#define maxn 300005
#define put() putchar('\n')
#define Tp template<typename T>
#define Ts template<typename T,typename... Ar>
using namespace std;
Tp void read(T &x){
int f=1;x=0;char c=getchar();
while (c<'0'||c>'9') {if (c=='-') f=-1;c=getchar();}
while (c>='0'&&c<='9') {x=x*10+c-'0';c=getchar();}
x*=f;
}
namespace Debug{
Tp void _debug(char* f,T t){cerr<<f<<'='<<t<<endl;}
Ts void _debug(char* f,T x,Ar... y){while(*f!=',') cerr<<*f++;cerr<<'='<<x<<",";_debug(f+1,y...);}
#define gdb(...) _debug((char*)#__VA_ARGS__,__VA_ARGS__)
}using namespace Debug;
#define fi first
#define se second
#define mk make_pair
const int mod=1e9+7;
int power(int x,int y=mod-2) {
int sum=1;
while (y) {
if (y&1) sum=sum*x%mod;
x=x*x%mod;y>>=1;
}
return sum;
}
int n,a[maxn],f[maxn];
int s[maxn],ans;
struct BIT {
#define lowbit(x) ((x)&(-(x)))
int f[maxn];
void add(int x,int y) {x++;for (;x<=n+1;x+=lowbit(x)) f[x]=max(f[x],y);}
int query(int x) {int sum=0;x++;for (;x;x-=lowbit(x)) sum=max(sum,f[x]);return sum;}
}t1,t2;
signed main(void){
int i;char ch;
read(n);
for (i=1;i<=n;i++) read(a[i]);
for (cin>>ch,i=1;i<n;i++) {
s[i]=(ch=='U');
ch=getchar();
}
for (i=1;i<=n;i++) {
f[i]=max(t1.query(a[i]),t2.query(n-a[i]+1))+1;
if (s[f[i]]) t1.add(a[i],f[i]);
else t2.add(n-a[i]+1,f[i]);
ans=max(ans,f[i]);
}
printf("%d\n",ans-1);
return 0;
}
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