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

int l[5005],w[5005];
int dp[5005];

int main()
{
	int n;
	scanf("%d",&n);
	for(int i=1;i<=n;i++)scanf("%d%d",&l[i],&w[i]);
	memset(dp,0x3f,sizeof(dp));
	dp[1]=1;
	for(int i=2;i<=n;i++)
	{
		if(l[i-1]>=l[i]&&w[i-1]>=w[i])dp[i]=dp[i-1];
		else dp[i]=dp[i-1]+1;
		for(int j=2;j<i;j++)
		{
			if(l[i-j]>=l[i]&&w[i-j]>=w[i])dp[i]=min(dp[i],dp[i-j]);
			else dp[i]=min(dp[i],dp[i-j]+1);
		}
	}
	printf("%d\n",dp[n]);
	return 0;
}