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#include<cstdio>
#include<iostream>
#include<cstring>
using
namespace
std;
int
Hash[10000];
int
main()
{
int
L,M,i,j;
while(scanf("%d%d",&L,&M)!=EOF){
int
a,b;
int
count=0;
for(i=0;i<=L;i++){
Hash[i]=1;
}
for(i=0;i<M;i++){
scanf("%d%d",&a,&b);
for(j=a;j<=b;j++){
Hash[j]--;
}
}
for(i=0;i<=L;i++){
if(Hash[i]==1){
count++;
}
}
printf("%d\n",count);
}
return
0;
}
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