#include <stdio.h>

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

	f1 = fopen("fact.in", "rt");
	f2 = fopen("fact.out", "wt");
	fscanf(f1, "%d", &p);

	if (p < 0) {
		fprintf(f2, "-1");
	}
		else {
			
			while (nr != p) {
				n = i;
				c = 0;
				while(n % 5 == 0) {
					c++;
					n = n / 5;
				}
				nr += c;
				i++;
			}

			if (i > 1) { 
				fprintf(f2, "%d", --i);
			}
			else {
				fprintf(f2, "1");
			}
		}
	
	fclose(f1);
	fclose(f2);

	return 0;
}