import std.stdio, std.string, std.conv
	,std.array, std.algorithm;

void main(){
  auto N = readln().strip().to!int();
  int[11] fl;

  foreach(immutable int i; 0 .. N) {
    auto ln = readln().strip().split().map!(to!int)();
    foreach(immutable int j; 0 .. 3)
      ++ fl[ln[j]];
  }

  int i2 = reduce!("a + b/2")(0, fl);
  writeln(i2 + (3*N - 2*i2)/4);

}