#include<stdio.h>
#include<math.h>

long nr0(long x) {
	long k = 5, nr = 0;
	while(x > k) {
		nr += x / k;
		k *= 5;
	}
	return nr;
}

int main() {
	FILE *f = fopen("fact.in", "r");
	FILE *g = fopen("fact.out", "w");
	
	long p;
	
	fscanf(f, "%ld", &p);
	
	long s = 0, d = 100000;
	while(s != d) {
		long m = (s + d) / 2; 
		if(p <= nr0(m)) {
			d = m;
		}
		else {
			s = m + 1;
		}
	}
	
	if(nr0(s) == p) fprintf(g, "%ld", s);
	else fprintf(g, "-1");
	
	fclose(f);
	fclose(g);
	
	return 0;
}