#include <iostream>
#include <fstream>

using namespace std;

int main()
{
    int n,p=0;
    ifstream f("fact.in");
    f>>n;int i=0;
    f.close();
    int v[2]={0,0};
    while(p<n)
    {
        if(i%2==0)v[0]++;
        if(i%5==0)v[1]++;
        if(v[0]>0&&v[1]>0)
        {
        p++;
        v[0]--;
        v[1]--;
        }
        i++;
    }
    ofstream g("fact.out");
    if(i==0)g<<1;
    else g<<i-1;
    return 0;
}