"use strict";
function I(t,i){this._s=t.split("\n"),this._c=0,this._l=0,this._f=i||Number}I.prototype.a=function(t){var i=this._s[this._l];if(i){var s=i.trim().split(" "),h=s[this._c];return this._c++,s.length===this._c&&(this._c=0,this._l++),t?t(h):this._f(h)}},I.prototype.l=function(t){var i=this._s[this._l];if(i)return this._c=0,this._l++,i.split(" ").map(t||this._f)},module.exports=I;

function main(input) {
  var o = new I(input);

  var n = o.a();
  var m = o.a();
  var low = 0, high = 100000;
  for (var i = 0; i < m; i++) {
    var l = o.a();
    var r = o.a();
    if (l > low) low = l;
    if (r < high) high = r;
  }

  console.log(high >= low ? high - low + 1 :0);
}


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