#include<cstdio>

using namespace std;

long long p, d, mini=-1, a=1, b=1000000001, c, e;
int main()
{       
    freopen ("fact.in","r",stdin);
    freopen ("fact.out","w",stdout);
	scanf("%lld",&p);
        while(a<=b)
	{
		c=a+(b-a)/2;
		d=c;
	       	e=0;
		while(d!=0)
		{
			d/=5;
			e+=d;
		}
		if(  e < p ) a=c+1;
		if( e > p ) b=c-1;
		if(e==p)  mini = c, b = c-1;
	
	}
	printf("%lld",mini);
	return 0;
}