https://cdn.luogu.com.cn/upload/image_hosting/0nqchcr8.png (在线IDE运行结果)
https://cdn.luogu.com.cn/upload/image_hosting/uh1xrvtp.png (本地运行结果)
#include<bits/stdc++.h>
using namespace std;
long long l,m,M,sum,i=0,n=0;
int main(){
cin>>l>>m;
M=m;
sum=l+1;
long long suma[sum],u[m],v[m];
for(int j=0;j<sum;j++){
suma[j]=1;
}
while(m>0){
cin>>u[m]>>v[m];
m--;
}
while(i<sum){
m=M;
while(m>0){
if(i>=u[m]&&i<=v[m]){
suma[i]=0;
}
m--;
}
i++;
}
i=0;
while(i<sum){
n+=suma[i];
i++;
}
cout<<n<<endl;
return 0;
}