var GET=(function(){function f(s){return new g(s);}function g(s){this._s=s.trim().split("\n");this._y=0;}g.prototype.a=function(f){var s=this._s, y=this._y, r;if(typeof s[y]==="string")s[y]=s[y].split(" ").reverse();r=s[y].pop();if(!s[y].length)this._y++;return f?r:+r;};g.prototype.l=function(f){var s=this._s[this._y++].split(" ");return f?s:s.map(a=>+a);};g.prototype.m=function(n,f){var r=this._s.slice(this._y,this._y+=n).map(a=>a.split(" "));return f?r:r.map(a=>a.map(a=>+a));};g.prototype.r=function(n,f){var r=this._s.slice(this._y,this._y+=n);return f?r:r.map(a=>+a);};return f;})();
var o=GET(require("fs").readFileSync("/dev/stdin","utf8"));

console.log(main());
function main(){
  var h = o.a();
  var w = o.a();
  var n = o.a();
  var b = Array(h+1);
  for(var i = 0; i <= h; i++)b[i] = {}, b[i][w+1] = 1;
  for(i = 0; i < n; i++){
    var t = o.l();
    b[t[1]][t[0]] = 1;
  }
  var ans = Object.keys(b[1])[0] - 1;
  var x = 2;
  for(i = 2; i <= h; i++){
    while(b[i][x])x++;
    if(x > ans)break;
    for(var j in b[i]){
      j = +j;
      if(x > j)continue;
      if(j - 1 < ans)ans = j - 1;
      break;
    }
    x++;
  }
  return ans;
}