FUleco

#include <bits/stdc++.h>

#define ll long long
#define for(i,a,n) for(int i=a; i<n; i++)
#define mms(matrica,n) memset(matrica,n,sizeof(matrica))
#define p_b push_back
#define m_p make_pair

using namespace std;

vector<int> sosedstvo[500000];
string s;
int n;
int dokaj=-1;
int node=0;
int parent[500000];

int poc, kra;
    int a,b;

void gradenje(int tem){

    dokaj++;
    if(dokaj==n)
        return;

    if(dokaj==a) poc=tem;
    else if(dokaj==b) kra=tem;


    if(s[dokaj]=='U'){
        node++;
        parent[node]=tem;
        sosedstvo[tem].p_b(node);
        sosedstvo[node].p_b(tem);
        gradenje(node);
    }
    else if(s[dokaj]=='D'){
        gradenje(parent[tem]);
    }
}

int main()
{
    mms(parent,-1);


    cin>>a>>b;
    cin>>s;
    n=s.size();
    parent[0]=0;
    gradenje(0);

//    for(i,0,10){
//        cout<<i<<endl;
//        for(j,0,sosedstvo[i].size()){
//            cout<<sosedstvo[i][j]<<" ";
//        }
//        cout<<endl<<endl<<endl;
//    }


    queue<pair<int, int>> q;
    q.push(m_p(poc,0));
    bool visited[node];
    mms(visited,0);
    visited[poc]=1;
    while(!q.empty()){

        int teme=q.front().first;
        int dist=q.front().second;
        q.pop();

        //cout<<teme<<endl;
        if(teme==kra){
            cout<<dist;
            return 0;
        }

        for(i,0,sosedstvo[teme].size()){
            int novo=sosedstvo[teme][i];
            if(!visited[novo]){
                q.push(m_p(novo,dist+1));
            }
        }
    }

//cout<<poc<<" "<<kra;
    return 0;
}