flappybird.cpp

// NOTE: it is recommended to use this even if you don't understand the following code.

#include <iostream>
#include <fstream>
#include <vector>

using namespace std;

// input data
long long N;
vector<long long> A, B;

int main() {
//  uncomment the following lines if you want to read/write from files
	ifstream cin("input.txt");
	ofstream cout("output.txt");

    cin >> N;
    A.resize(N);
    B.resize(N);
    for (long long i=0; i<N; i++)
        cin >> A[i] >> B[i];

    // insert your code here
    bool ans = true;
    for (long long y=0; y<N-1; y++) {
    	if (B[y]<A[y+1] || A[y]>B[y+1]) {
    		ans = false;
    		break;
		} else {
			ans = true;
		}
	}
	
	if (ans) {
		cout << "YES" << endl; // print the result
	} else {
		cout << "NO" << endl;
	}
    
    return 0;
}