#include <fstream>
using namespace std;
ifstream cin("fact.in");
ofstream cout("fact.out");
 
int p;
int zero(int m)
{
    int i, z=0;
    for(i=5; i<=m; i*=5) z+=m/i;
    return z;
}
 
int cautbin(int st, int dr)
{
    int m, z;
    while(st<=dr)
    {
        m=(st+dr)/2;
        z=zero(m);
        if(z==p && st==dr) return m;
        if(z==p) dr=m;
        else
            if(z<p) st=m+1;
            else dr=m-1;
    }
    return -1;
}
int main()
{
    cin>>p;
    cout<<cautbin(1, 500000000);
    return 0;
}