#include<stdio.h>
int factorial (int n){
	int s=0;
	while (n){
		s=s+n/5;
		n/=5;
	}
	return s;
}

int main (){
	int m, s, d, k;
	freopen ("fact.in", "r", stdin);
	freopen ("fact.out", "w", stdout);
	printf("k=");
	scanf("%d", &k);
	s=1;
	d=500000000;
	while(s!=d){
		m=(s+d)/2;
		if(factorial(m)>=k)
			d=m;
		else
			s=m+1;
	}
	if(factorial(s)==k)
		printf("%d", s);
	else
		printf("-1");
	fclose(stdin);
	fclose(stdout);
	return 0;
}