//a program that approximate e by computing values
#include <stdio.h>

	//factorial method
	float factorial(int n){
		if(n <= 1)
			return 1;
		else
			return n*factorial( n-1 );
		}

	//while loop that checks if the factorial is less than the num given
	int i = 2;
	while((1/factorial(i)) < num){
		result = result + (1/factorial(i));
		i++;
	}

int main(void)
{
	//initialise variables for use
	float num, result=2;

	//scan for the number
	scanf("%f", &num);

	//return the result with 5 decimals
	printf("%.5f\n", result);

	//return result
	return 0;
}