Blue Flag, White Flag

A flag flipping game is under way at the sports day held by the college student council. The software department and the ICT convergence department take turns playing. The rules are simple. The department whose turn it is sends out $N$ players. On the table in front of them sit $N$ flags numbered $1$ to $N$, each lying blue side up and white side down.

The first player turns over every flag whose number is a multiple of $1$. The second player turns over every flag whose number is a multiple of $2$. In the same way, the $i$-th player turns over every flag whose number is a multiple of $i$, and the game ends once the $N$-th player is done.

With $N$ players and $N$ flags, count the flags lying white side up after the $N$-th player has finished.

The first line contains $N$, the number of players and also the number of flags. ($1 \le N \le 2100000000$)

Print on the first line the number of flags lying white side up after the $N$-th player has finished.

Take $N = 3$. Flags $1$, $2$, $3$ are on the table and three players take part. The first player turns over every flag whose number is a multiple of $1$, so all three flags, blue side up at the start, end up white side up. The second player turns over flag $2$, the only multiple of $2$, leaving the flags white, blue, white. The last player turns over flag $3$, the only multiple of $3$, leaving them white, blue, blue. One flag lies white side up.