#include <fstream>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
long long check(long long x)
{
    long long nr0=0,h5=5;
    while(h5<=x)
    {
        nr0=nr0+x/h5;
        h5=h5*5;
    }
    return nr0;
}
int main()
{
    long long p,l,r,mid,sol;
    int ok;
    fin>>p;
    l=1;
    r=9223372036854775807;
    ok=1;
    while(l<=r)
    {
        mid=(l+r)/2;
        if(check(mid)<p){l=mid+1;}
        else{r=mid-1;sol=mid;ok=0;}
    }
    if(ok){fout<<"-1\n";}
    else{fout<<sol<<"\n";}
}