POJ 2665

 #include<iostream>
 #include<stdio.h>
 using namespace std;

 int main()
 {
     //freopen("acm.acm","r",stdin);
     int tree;
     int num;
     int sum;
     int a,b;
     while()
     {
     cin>>tree;
     cin>>num;
     if(!tree && !num)
         break;
     ++ tree;
     sum = ;
     while(num --)
     {
         cin>>a;
         cin>>b;
         sum += b - a + ;
     }
     cout<<tree - sum<<endl;
     }
 }