#pragma GCC optimize("Ofast")
#define _USE_MATH_DEFINES
#include "bits/stdc++.h"
using namespace std;

#define max(a, b) (a < b? b : a)
#define min(a, b) ((a>b)?b:a)

#define MOD 1000000007

#define FOR(a,c)   for ( ll (a)=0; (a)<(c); (a)++)
#define FORL(a,b,c)  for ( ll (a)=(b); (a)<(c); (a)++)
#define FORR(a,b,c)  for (  ll (a)=(b); (a)>=(c); (a)--)

#define INF 9223372036854775807
//18446744073709551615
#define abs llabs
#define by_ANIKET ios::sync_with_stdio(false);  cin.tie(NULL); cout.tie(NULL);

#define no cout<<"No\n";
#define yes cout<<"Yes\n";

#define Clear( a, b ) memset( a, b, sizeof( a ) )
#define run if(1)cout<<__LINE__<<endl;  

#define pr3(a,b,c) cerr<<#a<<"="<<a<<"\t"<<#b<<"="<<b<<"\t"<<#c<<"="<<c<<"\n";
#define pr2(a,b) cerr<<#a<<"="<<a<<"\t"<<#b<<"="<<b<<"\n";
#define pr1(a) cerr<<#a<<"="<<a<<"\n";
#define debug(x)       cerr<< #x <<" : "<< x << endl;
#define debuga(A,N)    cerr<< #A <<" : [";for(int i = 0; i<N;i++) cerr<<A[i]<<" "; cerr<<"]\n";
#define debuga2(A,N,M) cerr<< #A << " : \n"; for(int i=0;i<N;i++){cerr<<"[";for(int j=0;j<M;++j) cerr<<A[i][j]<<" ";cerr<<"]\n";}
#define debugp(p)      cerr<< #p <<" : "<<"("<<(p).first<<","<<(p).second<<")\n";
#define debugv(v)      cerr<< #v <<" : "<<"[";for(int i = 0; i< (v).size(); i++) cerr<<v[i]<<" "; cerr<<"]\n";
#define debugv2(v)     cerr<< #v << " : \n"; for(int i=0;i<v.size();i++){cerr<<"[";for(int j=0;j<(v[0].size());++j) cerr<<v[i][j]<<" ";cerr<<"]\n";}
#define debugs(m)      cerr<< #m <<" : [ "; for(auto itr = m.begin(); itr!=m.end();itr++) cerr<<*itr<<" "; cerr<<"]\n";
#define debugm(m)      cerr<< #m <<" : [ "; for(auto itr = m.begin();itr!=m.end(); itr++) cerr<<"("<<itr->first<<","<<itr->second<<") ";cerr<<"]\n";
typedef unsigned long long ull;
typedef long long int ll;
typedef vector<ll> vi;
typedef pair<ll,ll> pi;

#define F first
#define S second
#define PB push_back
#define POB pop_back
#define MP make_pair


inline long long  max3(long long  a, long long  b,long long  c){return (a)>(b)?((a)>(c)?(a):(c)):((b)>(c)?(b):(c));}
inline long long  min3(long long  a, long long b,long long c){return (a)<(b)?((a)<(c)?(a):(c)):((b)<(c)?(b):(c));}

ll powm(ll x,ll y,ll m=MOD)
{
	x=x%m;
	ll res=1;
	while(y)
	{
		if(y&1)
			res=(res*x)%m;
		y=y>>1;
		x=x*x;
		x%=m;
	}
	return res;
}
ll modFact(ll n, ll p=MOD) 
{ 
    if (n >= p) 
        return 0; 
  
    ll result = 1; 
    for (ll i = 1; i <= n; i++) 
        result = (result * i) % p; 
  
    return result; 
}
void solve()
{
	ll n,m,t=0,k=0,x=0,y=0,z=0,p,a1,a2,a3,a4,a5,ex,che,var=1,yd,f=INF,templ,tempr;
	cin>>n;
	char a[n];
	FOR(i,n){cin>>a[i];if(a[i]=='W')x++;else y++;}
	if(!x||!y)
	{
		cout<<"0\n";
		return;
	}
	FOR(i,y)
	{
		if(a[i]=='W')
			z++;
	}
	a1=z;
	z=0;
	cout<<a1<<"\n";

}

int main() 
{
	by_ANIKET
	ll T=1,t=0;
	//cin>>T;
	while(t++<T)
	{
		//cout<<"Case "<<t<<":"<<' ';
        solve();
        //cout<<'\n';
	}
	cerr << "Time : " << 1000 * ((double)clock()) / (double)CLOCKS_PER_SEC << "ms\n";
}
//   ©
//                      ______  __    __ ______ __    __ ________ ________ 
//                     /      \|  \  |  \      \  \  /  \        \        \
//                    |  ▓▓▓▓▓▓\ ▓▓\ | ▓▓\▓▓▓▓▓▓ ▓▓ /  ▓▓ ▓▓▓▓▓▓▓▓\▓▓▓▓▓▓▓▓
//  ______ ______     | ▓▓__| ▓▓ ▓▓▓\| ▓▓ | ▓▓ | ▓▓/  ▓▓| ▓▓__      | ▓▓   
// |      \      \    | ▓▓    ▓▓ ▓▓▓▓\ ▓▓ | ▓▓ | ▓▓  ▓▓ | ▓▓  \     | ▓▓   
//  \▓▓▓▓▓▓\▓▓▓▓▓▓    | ▓▓▓▓▓▓▓▓ ▓▓\▓▓ ▓▓ | ▓▓ | ▓▓▓▓▓\ | ▓▓▓▓▓     | ▓▓   
//                    | ▓▓  | ▓▓ ▓▓ \▓▓▓▓_| ▓▓_| ▓▓ \▓▓\| ▓▓_____   | ▓▓   
//                    | ▓▓  | ▓▓ ▓▓  \▓▓▓   ▓▓ \ ▓▓  \▓▓\ ▓▓     \  | ▓▓   
//                     \▓▓   \▓▓\▓▓   \▓▓\▓▓▓▓▓▓\▓▓   \▓▓\▓▓▓▓▓▓▓▓   \▓▓     

Measured memory_bytes: 3976