#include <iostream>
#include <vector>

using namespace std;

int main()
{
    int N, szml=0, i, j;
    cin>>N;
    string most, kell;
    cin>>most>>kell;
    //cout<<N<<" "<<most<<" "<<kell<<endl;
    //if (most[4]==kell[4]) cout<<"yes"<<endl;
    int m[N], k[N];
    for (i=0; i<N; i++)
    {
        if (most[i]=='S') m[i]=-1;
        else m[i]=1;
        if (kell[i]=='S') k[i]=-1;
        else k[i]=1;
    }
    for (i=N-1; i>-1; i--)
    {
        if (szml%2==0)
        {
            while (m[i]==k[i]) i--;
        }
        else
        {
            while (m[i]*-1==k[i]) i--;
        }
        if (i!=-1) szml+=1;
    }
    cout<<szml<<endl;
}