#ifndef _GLIBCXX_NO_ASSERT
#include <cassert>
#endif
#include <cctype>
#include <cerrno>
#include <cfloat>
#include <ciso646>
#include <climits>
#include <clocale>
#include <cmath>
#include <csetjmp>
#include <csignal>
#include <cstdarg>
#include <cstddef>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>

//#ifdef __GXX_EXPERIMENTAL_CXX0X__
#include <ccomplex>
#include <cfenv>
#include <cinttypes>
#include <cstdbool>
#include <cstdint>
#include <ctgmath>
#include <cwchar>
#include <cwctype>
//#endif

#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <locale>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <typeinfo>
#include <utility>
#include <valarray>
#include <vector>

#include <array>
//#include <atomic>
#include <chrono>
//#include <condition_variable>
#include <forward_list>
//#include <future>
#include <initializer_list>
//#include <mutex>
#include <random>
#include <ratio>
#include <regex>
#include <system_error>
//#include <thread>
#include <tuple>
#include <typeindex>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>

using namespace std;

const double EPS = 1e-8;
const double INF = 1e12;
typedef complex<double> P;
namespace std
{
	bool operator < ( const P& a , const P& b )
	{
		return real ( a ) != real ( b ) ? real ( a ) < real ( b ) : imag ( a ) < imag ( b );
	}
}
double cross ( const P& a , const P& b )
{
	return imag ( conj ( a )*b );
}
double dot ( const P& a , const P& b )
{
	return real ( conj ( a )*b );
}

struct L : public vector < P >
{
	L ( const P &a , const P &b )
	{
		push_back ( a ); push_back ( b );
	}
};

typedef vector<P> G;

struct C
{
	P p; double r;
	C ( const P &p , double r ) : p ( p ) , r ( r )
	{
	}
};

typedef complex<double> point;

int ccw ( P a , P b , P c )
{
	b -= a; c -= a;
	if( cross ( b , c ) > 0 )   return +1;       // counter clockwise
	if( cross ( b , c ) < 0 )   return -1;       // clockwise
	if( dot ( b , c ) < 0 )     return +2;       // c--a--b on line
	if( norm ( b ) < norm ( c ) ) return -2;       // a--b--c on line
	return 0;
}

vector<point> convex_hull ( vector<point> ps )
{
	int n = ps.size () , k = 0;
	sort ( ps.begin () , ps.end () );
	vector<point> ch ( 2 * n );
	for( int i = 0; i < n; ch[k++] = ps[i++] ) // lower-hull
		while( k >= 2 && ccw ( ch[k - 2] , ch[k - 1] , ps[i] ) <= 0 ) --k;
	for( int i = n - 2 , t = k + 1; i >= 0; ch[k++] = ps[i--] ) // upper-hull
		while( k >= t && ccw ( ch[k - 2] , ch[k - 1] , ps[i] ) <= 0 ) --k;
	ch.resize ( k - 1 );
	return ch;
}

int main ()
{
	int N;
	while( cin >> N , N )
	{
		vector<point>data ( N );
		for( size_t i = 0; i < N; i++ )
		{
			double a , b;
			char x;
			cin >> a >> x >> b;
			data[i] = P ( a , b );
		}
		auto y = convex_hull ( data );
		cout << ( N - y.size () ) << endl;
	}
}