#include <fstream>

using namespace std;

ifstream f("fact.in");
ofstream g("fact.out");
int zero(int x)
{
    int i,a=0,b=0,j;
    for(i=1;i<=x;i++)
    {
        j=i;
        while(j%2==0) {a++; j=j/2;}
        while(j%5==0) {b++; j=j/5;}
    }
    if (a>b) return b;
        return a;
}

int main()
{
    int p,i,n=1;
    f>>p;
    while(zero(n)!=p) n++;
    g<<n;
    return 0;
}