025_a_1.js

var
  lines     = [],
  readline  = require('readline').createInterface(process.stdin, process.stdout);

readline.on('line', function(line) {
  lines.push(line);
  if(lines.length === 2) {
    var chars = lines[0], charIndex = lines[1];
    for(var i = 0; i < chars.length; i++) {
      for(var j = 0; j < chars.length; j++) {
        var loopIndex = i * 5 + j + 1;
        if(loopIndex == charIndex ) {
          console.log(chars[i] + chars[j]);
        }
      }
    }
    process.exit(0);
  }
});