#include<fstream>
#include<math.h>
using namespace std;
int caut_fact(int z)
{
    int st=1,dr=5*(1e8);
    while(st<=dr)
    {
        int mid=(st+dr)/2;
        long long s=0,y=5;
        while(y<=mid)
        {
            s=s+mid/y;
            y=y*5;
        }
        if(z<=s)
        {
            dr=mid-1;
        }
        else
        {
            st=mid+1;
        }
    }
    return st;
}
int main()
{
    ifstream fin ("fact.in");
    ofstream fout ("fact.out");
    int x;
    fin>>x;
    fout<<caut_fact(x);
}