// yukicoder: No.436 ccw
// 2019.4.17 bal4u

#include <stdio.h>
#include <string.h>

#if 1
#define gc() getchar_unlocked()
#define pc(c) putchar_unlocked(c)
#else
#define gc() getchar()
#define pc(c) putchar(c)
#endif
int in()
{
	int n = 0, c = gc();
	do n = 10 * n + (c & 0xf), c = gc(); while (c >= '0');
	return n;
}

void outs(char *s) { while (*s) pc(*s++); }

#define N       1000000000
char *s = "1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859606162636465666768697071727374757677787980818283848586878889909192939495969798991";
int num[30];
int ans[30];
char _ans[200];

void mpStr2Num(int *num, char *str, int len)
{
	char *ss = str + len;
	int  *nn = num, k = 1, x = 0;

	do {
		x += (*--ss - '0') * k;
		k *= 10;
		if (k == N || ss == str) *++nn = x, x = 0, k = 1;
	} while (ss != str);
	*num = nn - num;
}

void mpNum2Str(char *str, int *num)
{
	int  i, j, x;
	char *ss;

	if (*num == 0 || (*num == 1 && *(num + 1) == 0)) {
		*str++ = '0', *str = '\0';
		return;
	}

	ss = str - 1;
	for (i = *num; i > 0; i--) {
		x = *++num;
		for (j = 1; j < N; j *= 10) {
			*++ss = x % 10 + '0';
			x /= 10;
		}
	} while (*ss == '0') ss--;

	*(ss + 1) = '\0';
	while (str < ss) {
		x = *str;
		*str++ = *ss;
		*ss-- = x;
	}
}

void mpMul(int *ret, int *a, int b)
{
	int  i, la, ca, *aa;
	long long x;

	la = *a;
	for (i = la + 1; i > 0; i--) *(ret + i) = 0;

	ca = 0;
	for (i = 1, aa = a; i <= la; i++) {
		x = *++aa;
		x = x * b + *(ret + i) + ca;
		*(ret + i) = x % N;
		ca = (int)(x / N);
	}
	*(ret + i) = ca;
	*ret = (ca != 0) ? la + 1 : la;
}

int main()
{
	int n;

	n = in();
	mpStr2Num(num, s, strlen(s));
	mpMul(ans, num, n);
	mpNum2Str(_ans, ans);
	if (n <= 8) pc('0'), pc('.'), outs(_ans);
	else if (n <= 81) pc(_ans[0]), pc('.'), outs(_ans+1);
	else pc(_ans[0]), pc(_ans[1]), pc('.'), outs(_ans + 2);
	pc('\n');
	return 0;
}