#include<cstdio>
#include<cmath>

int caut(int l, int r);
int nr5(int x);

using namespace std;
int n,y;
int main()
{
    freopen("fact.in","r",stdin);
    freopen("fact.out","w",stdout);
    scanf("%d",&n);
    y=caut(1,500000000);
    while(y%5!=0)
        y--;
    printf("%d",y);
    return 0;
}

int caut(int l, int r)
{
    int z,m;
    while(l<=r)
    {
        m=(l+r)/2;
        z=nr5(m);
        if(z==n&&l==r)
            return m;
        if(z==n)  r=m;
        else
        {
            if(z<n) l=m+1;
            else  r=m-1;
        }
    }
    return -1;
}

int nr5(int x)
{
    int nr,k;
    nr=5;
    k=0;
    while(nr<x)
    {
        k+=x/nr;
        nr*=5;
    }
    return k;
}