#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
int main()
{
int n, cnt = 0;
scanf("%d", &n);
string day1, day2;
cin >> day1 >> day2;
for (int i = 0; i < n; i ++ )
{
if(day1[i] == 'C' && day2[i] == 'C')
{
cnt ++;
}
}
printf("%d", cnt);
return 0;
}