#include <cstdio>

int zero(int n)
{
    int p=5,nr=0;
    while(n/p>0){nr+=n/p; p*=5;}
    return nr;
}

int cbin(int p)
{
    int l=1,r=100000000,m;
    while(l<r)
    {
        m=(l+r)/2;
        if(zero(m)>=p)r=m; else l=m+1;
    }
        if(zero(r)==p)return r;
        return -1;
}

int main()
{
    int p;
    freopen("fact.in","r",stdin);
    freopen("fact.out","w",stdout);
        scanf("%d",&p);

        printf("%d\n",cbin(p));

    return 0;
}