function main(input) {
  input=input.trim();
  const a = parseInt(input.split(" ")[0], 10);
  const b = parseInt(input.split(" ")[1], 10);
  const c = parseInt(input.split(" ")[2], 10);
  const d = parseInt(input.split(" ")[3], 10);
  if(c<b){
    if(a>c){
      console.log(b-a);
    }else{
      console.log(b-c);
    }
  }else{
    console.log(0);
  }

}
main(require('fs').readFileSync('/dev/stdin', 'utf8'));