"use strict";

function _slicedToArray(arr, i) { return _arrayWithHoles(arr) || _iterableToArrayLimit(arr, i) || _nonIterableRest(); }

function _nonIterableRest() { throw new TypeError("Invalid attempt to destructure non-iterable instance"); }

function _iterableToArrayLimit(arr, i) { var _arr = []; var _n = true; var _d = false; var _e = undefined; try { for (var _i = arr[Symbol.iterator](), _s; !(_n = (_s = _i.next()).done); _n = true) { _arr.push(_s.value); if (i && _arr.length === i) break; } } catch (err) { _d = true; _e = err; } finally { try { if (!_n && _i["return"] != null) _i["return"](); } finally { if (_d) throw _e; } } return _arr; }

function _arrayWithHoles(arr) { if (Array.isArray(arr)) return arr; }

!function () {
  function splitNum(line) {
    return (Array.isArray(line) ? line : line.split(/\s+/)).map(function (n) {
      return parseInt(n);
    });
  }

  !function (input) {
    var lines = input.split("\n");

    var _splitNum = splitNum(lines[0]),
        _splitNum2 = _slicedToArray(_splitNum, 2),
        N = _splitNum2[0],
        M = _splitNum2[1];

    var lrs = lines.slice(1, M + 1).map(function (line) {
      var _splitNum3 = splitNum(line),
          _splitNum4 = _slicedToArray(_splitNum3, 2),
          L = _splitNum4[0],
          R = _splitNum4[1];

      return {
        L: L,
        R: R
      };
    });
    var min = 1,
        max = N;
    var _iteratorNormalCompletion = true;
    var _didIteratorError = false;
    var _iteratorError = undefined;

    try {
      for (var _iterator = lrs[Symbol.iterator](), _step; !(_iteratorNormalCompletion = (_step = _iterator.next()).done); _iteratorNormalCompletion = true) {
        var _step$value = _step.value,
            L = _step$value.L,
            R = _step$value.R;
        if (L > min) min = L;
        if (R < max) max = R;
      }
    } catch (err) {
      _didIteratorError = true;
      _iteratorError = err;
    } finally {
      try {
        if (!_iteratorNormalCompletion && _iterator.return != null) {
          _iterator.return();
        }
      } finally {
        if (_didIteratorError) {
          throw _iteratorError;
        }
      }
    }

    console.log(Math.max(0, max - min + 1));
  }(require("fs").readFileSync("/dev/stdin", "utf8"));
}();
