#include <bits/stdc++.h>
using namespace std;
int main() {
// your code goes here
string s;
cin>>s;
set <pair<int,int>> st;
int n=s.size(),t=1e9;
int x=0,y=0,ans=0;
char dir=0;
for (int i=0;i<n;i++){
st.insert({x,y});
if (s[i]=='S'){
ans++;
if (dir==0){
y++;
}
if (dir==1){
x++;
}
if (dir==2){
y--;
}
if (dir==3){
x--;
}
if (st.find({x,y})!=st.end()&&ans!=0){
cout<<ans;
return 0;
}
}
if (s[i]=='L'){
dir=(dir==0? 3:(dir-1));
}
if (s[i]=='R'){
dir++;
dir%=4;
}
}
cout<<-1;
return 0;
}
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