#include <bits/stdc++.h>
using namespace std;
#ifdef __DEBUG__
    void debug_out() { cerr << endl; } 
    template <typename Head, typename... Tail>
    void debug_out(Head H, Tail... T) {cerr << " " << H; debug_out(T...);}
    #define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
    #define debug(...) 
#endif

using ll = long long int;
using ull = unsigned long long int;
using ld = long double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;

int dx[]={1, 0, -1, 0, 1,-1, 1,-1};
int dy[]={0, 1, 0, -1, 1, 1,-1,-1};
const int INT_INF = (int)(2e9);
const ll  LL_INF = (ll)(2e18);

inline void fast_io() { ios_base::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr); };
template<typename T, typename S> inline ostream& operator<<(ostream& os, const pair<T, S> p) { cout << "[" << p.first << ";" << p.second << "]"; return os; }
template<typename T, typename S> inline ostream& operator<<(ostream& os, const map<T, S> p) { for (auto el : p) cout << "[" << el.first << ";" << el.second << "]"; return os; }
template<typename T> inline ostream& operator<<(ostream& os, const vector<T>& v) { for (auto el : v) cout << el << " "; return os; }
template<typename T> inline ostream& operator<<(ostream& os, const deque<T>& v) { for (auto el : v) cout << el << " "; return os; }
template<typename T> inline ostream& operator<<(ostream& os, const set<T>& v) { for (auto el : v) cout << el << " "; return os; }
template<typename T> inline vector<T> fetch_vec(int sz) { vector<T> ret(sz); for (auto& elem : ret) cin >> elem; return ret; }

int N;
string s;
inline void input(){
    fast_io();
    cin >> N;
    cin >> s;
}

void fox(string &t){
    if(t.length() < 3) return;
    int n = t.length();
    if(t[n-1] == 'x' && t[n-2] == 'o' && t[n-3] == 'f'){
        t.pop_back();
        t.pop_back();
        t.pop_back();
    }
    return ;
}

inline int solve(){
    string t = "";
    for (int i = 0; i < N; i++)
    {
        t.push_back(s[i]);
        fox(t);
    }
    
    cout << t.length() << endl;
    return 0;
}   

int main()
{
    input();
    solve();
    return 0;
}

#include<bits/stdc++.h>
using namespace std;
#define     pb         push_back
#define     ff             first
#define     ss            second
#define     ll         long long
#define   rep(n) for(int i=0;i<n;i++)
void fastInOut() {
    ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
#ifndef ONLINE_JUDGE
    freopen("input.txt" , "r" , stdin);
    freopen("output.txt" , "w" , stdout);
#endif
}

void solve()
{
    int a , b; // a = solid , b = fat
    cin >> a >> b;
    a = a + b;
    if (a >= 15 && b >= 8)
    {
        cout << 1 ;
    }
    else if (a >= 10 && b >= 3)
    {
        cout << 2 ;
    }
    else if (a >= 3)
    {
        cout << 3;
    }
    else
    {
        cout << 4;
    }

}
int main(int argc, char const * argv[]) {
    fastInOut();
    int tc = 1;
    //cin >> tc;
    while (tc--)
    {
        solve(); cout << endl;
    }
}