#include <stdio.h>

#define MAX_NUMBER 4500000015
#define MIN_NUMBER 0

long normalizeToFive(long number) {
	while (number % 5 != 0) 
		number--;
	return number;
}

long factorialLeadingZeroesOf(long number) {
	long sum = 0;
	while (number >= 1) {
		sum += number / 5;
		number /= 5;
	}
	return sum;
}

long factorialZeroes(long zeroes) {
	long st = MIN_NUMBER, dr = MAX_NUMBER;

	while (st < dr) {
		long aux = (dr - st) / 3;
		long m1 = st + aux;
		long m1_zeroes = factorialLeadingZeroesOf(m1);
		if (m1_zeroes == zeroes)
			return normalizeToFive(m1);

		long m2 = dr - aux;
		long m2_zeroes = factorialLeadingZeroesOf(m2);
		if (m2_zeroes == zeroes)
			return normalizeToFive(m2);
		else if (m1_zeroes < zeroes && m2_zeroes < zeroes)
			st = m2 + 1;
		else if (m1_zeroes < zeroes && m2_zeroes > zeroes) {
			st = m1 + 1;
			dr = m2 - 1;
		} else 
			dr = m1 - 1;
	}
	
	return -1;
}

int main() {
	long p;
	char *inputFileName = "fact.in", *outputFileName = "fact.out";
	
	FILE *in = fopen(inputFileName, "r");
	if (in == NULL) {
		printf("Can't open input file with name \"%s\".\n", inputFileName);	
		return -1;
	}
	fscanf(in, "%ld", &p);
	fclose(in);

	FILE *out = fopen(outputFileName, "w");
	if (out == NULL) {
		printf("Can't create file with name \"%s\".\n", outputFileName);
	}
	fprintf(out, "%ld\n", factorialZeroes(p));
	fclose(out);

	return 0;
}