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                (J U S T   L I K E   E V E R Y O N E   E L S E !)

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*/                              
#include<bits/stdc++.h>
using namespace std;
 
#define fastio ios_base::sync_with_stdio(0); cin.tie(0)
#define LL long long 
#define mod 1000000007 
#define all(v) v.begin(),v.end()
#define FOR(i, j, k) for (auto i=j ; i<k ; i++)
#define ROF(i, j, k) for (auto i=j ; i>=k ; i--) 
#define debug(...) fprintf(stderr, __VA_ARGS__), fflush(stderr)
#define time__(d) for(long blockTime = 0; (blockTime == 0 ? (blockTime=clock()) != 0 : false); debug("%s time : %.4fs", d, (double)(clock() - blockTime) / CLOCKS_PER_SEC))

const long long INF = 1e18;
const long long MAX = 1e5+10;
int main(){
    fastio;
    int t=1;//s cin>>t;
    while(t--){
        int n; cin>>n; string  s; cin>>s;
        int ans = 0;
        FOR(i,0,n) {
            int r=0,w=0,j=i;
            while(j<n && s[j]=='W') j++,w++;
            while(j<n && s[j]=='R') j++,r++;
            if(w && r) ans+=r;
            i=j-1;
        }
        int i =0,j=n-1,p=0;
        while(i<j) {
            while(i<n && s[i]=='R') i++;
            while(j>=0 && s[j]=='W') j--;
            if(i<j) p++;
            i++,j--;
        }ans =min(p,ans);
        int r=0,w=0; //cout<<ans<<" ";
        FOR(i,0,n) if(s[i]=='R') r++; else w++;
        ans = min(ans,w);
        cout<<ans;
    }
}


Measured memory_bytes: 3736