#include<bits/stdc++.h>
using namespace std;
const long long MaxN = 1e5 + 5;
pair<long long, long long> pr[MaxN];
long long n;
int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    if (fopen("suml.inp", "r"))
    {
        freopen("suml.inp", "r", stdin);
        freopen("suml.out", "w", stdout);
    }
    cin >> n;
    for (long long i=1; i<=n; i++)
    {
        cin >> pr[i].first >> pr[i].second;
        if(pr[i].second !=0)
        {
            pr[i].second += (pr[i].first-1);
        }
        else
        {
            pr[i].second = pr[i].first;
        }
    }
    sort(pr+1,pr+n+1);
    long long ans = pr[1].second - pr[1].first +1;
    long long l = pr[1].first, r=pr[1].second;
    for (long long i=2; i<=n; i++)
    {
        if(r<pr[i].first)
        {
            l = pr[i].first, r=pr[i].second;
            ans += r-l+1;
        }
        if(r>=pr[i].first)
        {
            if(pr[i].second <= r) continue;
            ans += (pr[i].second - r);
            r = pr[i].second;
        }
    }
    cout << ans;
}