How to convert large number string into integers in jsr223 sampler with groovy

I am using a jsr223 sampler to read jtl file and break it into multiple files, cant use csv data set configure for some reason. I am using groovy as language

def INPUT_FILE = vars.get("INPUT_FILE");
def lines = new File(INPUT_FILE).readLines();
int start = lines[1].split(',')[0].toInteger(); //taking second line first column and converting to int
log.info("=====read start: " + start); //displaying in logs

This is giving error, unable to figure out the fix, tried out with long, def data types