#include <fstream>
using namespace std;
#define MAX 100003
int p;
int nzero(int x)
{
    int rez=0,p5=5;
    while(x/p5 >0)
    {
        rez=rez+x/p5;
        p5=p5*5;
    }
    return rez;
}
int main()
{
    ifstream fin("fact.in");
    ofstream fout("fact.out");
    fin>>p;
    int st = 1, dr = 5*100000000;
    while(st<=dr){
        int mij = (st+dr)/2;
        if(nzero(mij)<p)
            st = mij + 1;
        else
            dr = mij - 1;
    }
    fout<<st;
    return 0;
}