#include<cstdio>
#include<algorithm>

using namespace std;

  int d[200050];
  int s[200050];
  int t[200050];
  bool f[200050];
  int n;
  int tot;
  int sum=0;

int main(){
  freopen("boarding.in","r",stdin);
  freopen("boarding.out","w",stdout);
  
  scanf("%d",&n);
  for (int i=1;i<=n;i++){
    scanf("%d%d",&s[i],&t[i]);
    d[i]=i-n;
  }
  
  while (sum!=n){
    tot++;
    for (int i=n;i;i--){
      if (f[i]){
        continue;
      }
      if (d[i]==s[i]){
        if (t[i]){
          t[i]--;
          if (!t[i]){
            sum++;
            f[i]=1;
            d[i]=0x3f3f3f3f;
          }
        }
        else{
          continue;
        }
      }
      else{
        if (d[i+1]!=d[i]+1){
          d[i]++;
        }
      }
    }
  }

  printf("%d\n",tot+1);
  
  return 0;
}