11661

#include <iostream>
#include <cstdio>
#include <sstream>
#include <string>
#include <cstring>

using namespace std;

char s[2000000+10];

int main()
{
	int n,dist,prev_idx;
	char prev;
	bool first;
	while(scanf("%d",&n),n)
	{
		dist= n;
		first=0;
		scanf("%s",s);
		for(int i=0;i<n;i++)
		{
			//scanf("%c",&s[i]);
			if(s[i]=='Z')
			dist=0;
			if(s[i]=='R' && first==false)
			{
				prev='R';
				prev_idx=i;
				first=true;
				continue;
			}
			if(s[i]=='D' && first==false)
			{
				prev='D';
				prev_idx=i;
				first=true;
				continue;
			}
			if(first==1 && (s[i]=='D' || s[i]=='R'))
			{
				if(prev==s[i])
				{
					prev_idx=i;
				}
				else
				{
					if(dist>(i-prev_idx))
					dist=i-prev_idx;
					prev=s[i];
					prev_idx=i;
				}
			}
		}//for ends
		printf("%d\n",dist);
	}
	return 0;
}