#include<stdio.h>

int div(int n, int i)
{
    int s=0;
    while(n%i==0)
    {
        n/=i;
        ++s;
    }
    return s;
}

int min(int a,int b)
{
    if(a<=b)
        return a;
    else
        return b;
}
int main()
{
    freopen("fact.in","r",stdin);
    freopen("fact.out","w",stdout);

    int s1=0,s2=0,i=1,p;

    scanf("%d", &p);

    while(min(s1,s2)<p)
        {
            if(i%2==0)
                s1=s1+div(i,2);
            if(i%5==0)
                s2=s2+div(i,5);
            ++i;

        }

    printf("%d", i-1);
    return 0;

}