import std.stdio, std.algorithm, std.conv, std.array, std.string, std.math, std.typecons, std.numeric;

void main()
{
    auto X = readln.chomp.to!int;
    auto i = 1;
    for (;;) {
        if ((i+1)^^2 > X) break;
        ++i;
    }
    writeln(i^^2);
}