#include<cstdio>
using namespace std;
long long k,p,u;
long long zero(long long n)
{
    long long k=5,s=0;
    while(k<=n)
    {
        s+=n/k;
        k *= 5;
    }
        return s;
}

int main()
{
    freopen("fact.in","r",stdin);
    freopen("fact.out","w",stdout);
    scanf("%lld",&p);
    k=1;u=5*p;

    while(k<=u)
    {
        long long mid=(u+k)/2;
        if(zero(mid)>=p)
            u=mid-1;
        else
            k=mid+1;
    }

    if(zero(k)==p)
        printf("%lld",k);
    else
        printf("-1");

    return 0;
}