#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cmath>
#include<cstring>
using namespace std;
struct node{
	int l,r;
}a[1001000];//记录每个节点的左右节点
int ans,n;
bool pass;
int main(){
	cin>>n;//输入n
	for(int i=1;i<=n;i++){
		cin>>a[i].l>>a[i].r;
		if(a[i].l!=0)ans++;
		if(a[i].l==0&&!pass)ans++;
	}
	cout<<ans;
	return 0;
}

//都这样了我都能骗分