#include<cstdio>
#define N 1000000000
int n;
void citire()
{
	freopen("factorial.in","r",stdin);
	freopen("factorial.out","w",stdout);
	scanf("%d",&n);
}
int zero(int x)
{
	int r=0;
	while (x)
	{
		x/=5;
		r+=x;
	}
	return r;
}
int caut()
{
	int st=1,dr=N;
	while (st!=dr)
	{
		int m=(st+dr)/2;
		if (zero(m)>=n)
			dr=m;
		else
			st=m+1;
	}
	if (zero(st)!=n)
		return -1;
	return st;
}
int main()
{
	citire();
	printf("%d",caut());
	return 0;
}