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