#include "bits/stdc++.h"
using namespace std;

#define FOR(i,a,b) for (int i = (a); i < (b); i++)
#define RFOR(i,b,a) for (int i = (b) - 1; i >= (a); i--)
#define ITER(it,a) for (__typeof(a.begin()) it = a.begin(); it != a.end(); it++)
#define FILL(a,value) memset(a, value, sizeof(a))

#define SZ(a) (int)a.size()
#define ALL(a) a.begin(), a.end()
#define PB push_back
#define MP make_pair

typedef long long Int;
typedef vector<int> VI;
typedef pair<int, int> PII;

const double PI = acos(-1.0);
const int INF = 1000 * 1000 * 1000;
const Int LINF = INF * (Int) INF;
const int MAX = 1000007;

const int MOD = 998244353;

Int vm(PII A, PII B, PII C) {
    return 1LL * (B.first - A.first) * (C.second - A.second) - 1LL * (B.second - A.second) * (C.first - A.first);
}

Int sc(PII A, PII B, PII C) {
    return 1LL * (B.first - A.first) * (C.first - A.first) + 1LL * (B.second - A.second) * (C.second - A.second);
}

int sgn(Int x) {
    if (x > 0) return 1;
    if (x < 0) return -1;
    return 0;
}

Int vm(PII A, PII B, PII C, PII D) {
    Int x1 = B.first - A.first;
    Int y1 = B.second - A.second;
    Int x2 = D.first - C.first;
    Int y2 = D.second - C.second;
    return x1 * y2 - x2 * y1;
}

Int sc(PII A, PII B, PII C, PII D) {
    Int x1 = B.first - A.first;
    Int y1 = B.second - A.second;
    Int x2 = D.first - C.first;
    Int y2 = D.second - C.second;
    return x1 * x2 + y1 * y2;
}

int main(int argc, char* argv[])
{
	int n;
    cin >> n;
    vector<PII> A(n);
    FOR(i,0,n){
        int x, y;
        cin >> x >> y;
        A[i] = MP(x, y);
    }

    int res = 1;

    int l = 0;
    int r = 1;
    while (r + 1 < n) {
        if (vm(A[l], A[r], A[r + 1]) == 0 && sc(A[l], A[r], A[r + 1]) >= 0)
            ++ r;
        else
            break;

    }

    while (r + 1 < n) {
        ++ res;
        int ll = r + 1;
        int rr = ll;
        while (rr + 1 < n) {
            if (ll == rr && vm(A[l], A[r], A[ll]) != 0 && vm(A[l], A[r], A[ll], A[ll + 1]) == 0)
                break;


            if (vm(A[ll], A[rr], A[rr + 1]) == 0 &&
                sc(A[ll], A[rr], A[rr + 1]) >= 0 &&
                sgn(vm(A[l], A[r], A[ll])) * sgn(vm(A[l], A[r], A[rr + 1])) != -1 &&
                sgn(vm(A[ll], A[rr + 1], A[l])) * sgn(vm(A[ll], A[rr + 1], A[r])) != -1
                && sc(A[l], A[r], A[rr + 1], A[ll]) > 0)
                ++ rr;
            else
                break;
        }
        l = ll;
        r = rr;
        if (l == r) -- l;
        cerr << l << ' ' << r << endl;
    }
    cout << res << endl;

	cerr << 1.0 * clock() / CLOCKS_PER_SEC << endl;
}