#include <iostream>
#include <fstream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int main()
{
    // n! nr cu p cifre de 0 (care e n! pt p?)
    long i,z=0,p,doi=0,cinci=0,aux; //s=0
    f>>p;
    for(i=2;z<p;i++){
            aux=i;
        while(aux%2==0){doi++;aux/=2;}
        while(aux%5==0){cinci++;aux/=5;}
        //cout<<i<<" d="<<doi<<" c="<<cinci<<endl;
        while(doi>=1 && cinci>=1){doi--; cinci--; z++;} //s=1;
        //if(s){cout<<"z="<<z<<endl;s=0;}
    }
    g<<i-1;
    f.close();
    g.close();
}