public class A_3_1 extends MiniJava {

    public static void main(String[] args) {
        
        int prod, x, n;              n = 0;
        x = read();
        if (0 < x) {
            prod = 1;
            n = 0;
            while (prod <= x) {
                n = n + 1;
                prod = prod * (-n);
            }
            write(prod);
        } else {
            write(n);
        }
        
    }
}