#include <iostream>

using namespace std;

int main()
{
    int p,n,i,s,x,pu;
    cin>>p;
    x=0;
    s=0;
    while (s!=p)
    {
        s=0;
        pu=5;
        for (i=1;i<=10000;i++)
        {
            s=s+x/pu;
            pu=pu*5;
            if (pu>x)
                break;
        }
        x=x+5;
    }
    cout<<x-5;
    return 0;
}