#include <cstdio>
using namespace std;

long long zero(long long n)
{
    long long z=0,t;
    long long p=5;
    while (p<=n)
    {
        t=n/p;
        z=z+t;
        p=p*5;
    }
    return z;
}

int main()
{
    freopen("factorial.in","r",stdin);
    freopen("factorial.out","w",stdout);
    int n;
    scanf("%d",&n);
    int ls=1;
    long long ld=100000000000,m,p;
    while (ls<ld)
    {
        m=(ls+ld)/2;
        if (zero(m)<p) ls=m;
        else ld=m;
    }
    if (zero(ls)==p)
    {
        printf("%ll",ls);
    }
    else printf("%d",-1);
    return 0;
}