function Main(input) {
    var n = parseInt(input, 10);
    var j = 1;
    var i = 1;
    var k = [];
        while(n >= i) {
        var i = Math.pow(j, 2);
        k.push(i);
        j++
    }
    console.log(k[k.length-2]);
    }
Main(require('fs').readFileSync('/dev/stdin', 'utf8'));