#include <iostream>
#include <utility>
#include <cmath>
using namespace std;
long double cross(pair<long double, long double> a, pair<long double, long double> b){return a.first*b.second-a.second*b.first;}
long double dot(pair<long double, long double> a, pair<long double, long double> b){return a.first*b.first+a.second*b.second;}
int main(){
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    pair<long double, long double> bef={0, 1}, nw;
    long long i, n, angle, ans=0; cin >> n;
    long double sum=0;
    for(i=0; i<n; ++i){
        cin >> nw.first >> nw.second;
        sum+=atan2(cross(nw, bef), dot(nw, bef));
        swap(nw, bef);
    }
    sum*=360.0;
    sum/=6.2831853072;
    angle=round(sum);
    if(angle>0){
        ans=angle/360;
        angle%=360;
    } else{
        ans-=abs(angle)/360;
    }
    cout << ans;
    return 0;
}