#include <stdio.h>

inline int numar(int n)
{
	if (n % 5 != 0)
		return 0;

	int c = 0;
	while(n % 5 == 0) {
		c++;
		n = n / 5;
	}

	return c;
}

int main(void)
{
	int p, i = 1, nr = 0, gata = 1;
	FILE *f1, *f2;

	f1 = fopen("fact.in", "rt");
	f2 = fopen("fact.out", "wt");
	if (f1 == NULL || f2 == NULL) {
		printf("E jale\n");
	}
	fscanf(f1, "%d", &p);

	if (p < 0) {
		fprintf(f2, "-1");
	}
		else {
			while (nr != p) {
				nr += numar(i);
				i++;
			}
			fprintf(f2, "%d", --i);
		}
	
	fclose(f1);
	fclose(f2);

	
}