#include <cstdio>
#include <fstream>
using namespace std;
const long long NMAX=1e7;
int main()
{
    freopen("fact.in","r",stdin);
    freopen("fact.out","w",stdout);
    long long n,st,dr,med,ans=-1;
    scanf("%lld",&n);
    st=1;
    dr=NMAX;
    while(st<=dr)
    {
        med=(st+dr)/2;
        long long p=5,a=0;
        while(p<=n)
        {
            a+=n/p;
            p*=5;
        }
        if(a==n)
        {
            dr=med-1;
            ans=med;
        }
        else if(a>n)
            dr=med-1;
        else
            st=med+1;
    }
    if(ans==-1)
        printf("-1");
    else
        printf("%lld",ans);
    return 0;
}