#include <stdio.h>
int f(int k){
	int i=0;
	do{
		i+=k/5;
		k=k/5;
	}while(k);
	return i;
}
int main(){
	int k,a=1,b=500000000,m;
	freopen("fact.in","r",stdin);
	freopen("fact.out","w",stdout);
	scanf("%d",&k);
	while(a!=b){
		m=(a+b)/2;
		if(f(m)>=k)
			b=m;
		if(f(m)<k)
			a=m+1;
	}
	if(f(a)==k)
		printf("%d\n",a);
	else
		printf("-1\n");
	fclose(stdin);
	fclose(stdout);
	return 0;
}