为什么有两个点 RE

#include <bits/stdc++.h>
using namespace std;
int n , m , a[120000] , num ;
int x ,maxx;
int main()
{
    scanf ("%d",&x);
    for (int i = 1 ; i <= x ; i ++ ){
        scanf ("%d%d",&n,&m);
        maxx = max (m , maxx);
        for (int j = n ; j <= m ; j ++ )
            a[j] = 1 ;
    }
    for (int i = 1 ; i <= maxx ; i ++ )
        if (a[i] == 1 )
            num ++ ;
    printf("%d",num );
    return 0;
}