#include<bits/stdc++.h>
#define maxn 100005
using namespace std;
int n,L[maxn],R[maxn],ans,dp[maxn],maxx;
bitset<maxn>f;
signed main(){
    // freopen("lis.in","r",stdin);
	// freopen("lis.out","w",stdout);
    ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
	cin>>n;for(int i=1;i<=n;++i)cin>>L[i]>>R[i];f[0]=1;
    for(int i=1;i<=n;++i){
        for(int j=R[i];j<=maxx;++j)if(f[j]){f[j]=0;break;}
        for(int j=R[i]-1;j>=L[i];--j)f[j+1]=f[j];f[L[i]]=1;
        maxx=max(maxx,R[i]);
    }
    for(int i=1;i<=maxx;++i)if(f[i])ans++;
    cout<<ans;
	return 0;
}