#include <stdio.h>
int main(int argc, char* argv[]){ int length,many; int i; int start,end; int sum=0;
scanf("%d %d",&length,&many);
while(length !=0 && many != 0) { length += 1;
for(i=0;i<many;i++) { scanf("%d %d",&start,&end); length -= (end-start)+1; }
printf("%d/n",length);
scanf("%d %d",&length,&many);
}
return 0;
}
