<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> 
  
 Вес атлета 
 <input id="AthleteWeight"></input> 
 <br> 
 Поднятый вес 
 <input id="WeightLifted"></input> 
 <br> 
 Количество движений (1 или 2) 
 <input id="LiftNum"></input> 
 <br> 
  
 <script> 
 function k() 
 { 
 var result; 
 var text1 = document.getElementById("AthleteWeight").value; 
 var text2 = document.getElementById("WeightLifted").value; 
 var text3 = document.getElementById("LiftNum").value; 
 result = (+(text2) + (+(text1)) * 0.85 * (+(text3))) / Math.pow(+(text1), 2.0/3.0)  
 alert(result) 
 } 
 </script> 
  
 <button onclick="k()">Найти коэффициент</button>

 
 <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> 
  
 Вес атлета 
 <input id="AthleteWeight"></input> 
 <br> 
 Поднятый вес 
 <input id="WeightLifted"></input> 
 <br> 
 Количество движений (1 или 2) 
 <input id="LiftNum"></input> 
 <br> 
  
 <script> 
 function k() 
 { 
 var result; 
 var text1 = document.getElementById("AthleteWeight").value; 
 var text2 = document.getElementById("WeightLifted").value; 
 var text3 = document.getElementById("LiftNum").value; 
  
 // put dots instead of commas 
 var _AthleteWeight = parseFloat(text1.replace(",", ".")); 
 var _WeightLifted = parseFloat(text2.replace(",", ".")); 
 var _LiftNum = parseFloat(text3.replace(",", ".")); 
  
 result = (_WeightLifted + _AthleteWeight * 0.85 * _LiftNum) / Math.pow(_AthleteWeight, 2.0/3.0)  
 alert(result) 
 } 
 </script> 
  
 <button onclick="k()">Найти коэффициент</button>