#include <fstream>

using namespace std;

ifstream fin("fact.in");
ofstream fout("fact.out");

int verif(int n){
    int pc=5,cinci=0;
    while(n/pc>0)
        cinci+=n/pc,pc=pc*5;
    return cinci;
}

int main()
{
    int inc=1,sf,p,m;
    fin>>p;
    sf=p*5;
    while(inc<=sf){
        m=(inc+sf)/2;
        if(verif(m)<p)
            inc=m+1;
        else
            sf=m-1;
    }
    if(verif(inc)==p)
        fout<<inc;
    else
        fout<<-1;

    return 0;
}