#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
using namespace std;
int main ()
{
    vector <int > distance ;
    int highway , x , num;
    string s;
    bool foun_Z=false;
    while(cin>>highway)
    {
        if(highway==0)
        {
            break;
        }
             cin>>s;
            for(int i=0 ; i< s.size() ; i++)
            {
                if(s[i]=='Z')
                {
                        foun_Z=true;
                        cout<<0<<endl;
                        break;
                }
                else if(s[i]=='R')
                {
                    num=s.find('D',i);
                    if(num>=0)
                    {
                        distance.push_back(num-i);
                    }
                    num=s.rfind('D',i);
                    if(num>=0)
                    {
                        distance.push_back(i-num);
                    }
                }
            }
            if(foun_Z==false)
            {
                sort(distance.begin() ,distance.end());
                cout<<distance.front()<<endl;
            }
            distance.clear();
            foun_Z=false;
    }
return 0;
}