#include <fstream>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int i , j, c, x, y, p, k, st, dr, mid;
int main()
{
    fin>>p;
    if(p==1){
        fout<<5;
        return 0;
    }
    if(p==0){
        fout<<1;
        return 0;
    }
    st=1;
    dr=20000000;
    while(st<=dr){
        mid=(st+dr)/2;
        x=5;y=0;
        while(x<=5*mid){
            y+=5*mid/x;x=5*x;
        }
        //fout<<y<< " ";
        if(p==y)
            break;
        else{
            if(p>y)
                st=mid+1;
            else
                dr=mid-1;
        }

    }
    if(st<=dr)
        fout<<5*mid;
    else
        fout<<-1;
    return 0;
}