#include <fstream>
#include <iostream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int main()
{   long long p,n=0;
    f>>p;
    f.close();
    long long i,j,nr;
    for(i=5;n<p;i+=5)
        {j=i; nr=0;
        while(j%5==0)
            {nr++;
            j/=5;
            }
        n+=nr;
        }
    g<<i-5;
    g.close();
    return 0;
}