代码:
#include <cstdio>
#include <fstream>
#include <algorithm>
#include <cstring>
#include <string>
#include <iostream>
using namespace std;
const int maxl = 10010;
int main(){
// freopen("a.txt", "r", stdin);
int l, m;
int hash[maxl];
int start, end;
while(cin >> l >> m){
memset(hash, -1, (l + 1) * sizeof(int));
for(int i = 0; i < m; ++i){
cin >> start >> end;
for(int i = start; i <= end; ++i){
hash[i] = 0;
}
}
int sum = 0;
for(int i = 0; i < l + 1; ++i){
sum += hash[i];
}
cout << -sum << endl;
}
return 0;
}