#include<stdio.h>

int main()
{
    int type,number,ans = 0,id=0;
    int showup[1005]={};
    while(scanf("%d%d",&type,&number)==2 && (type!=-1&&number!=-1) )
    {
        if(type == 1)
        {
            showup[number] += 1;
            ans+=1;
        }
        else
        {
            ans -= showup[number];
            showup[number] = 0;
        }
    }
    printf("%d\n",ans);
}