#include<cstdio>
using namespace std;
int n,p;
int zerouri(int x)
{
    int s=0;
    int k=5;
    while(k<=x)
    {
        int a=x/k;
        s+=a;
        k*=5;
    }
    return s;
}
int cautbin(int val)
{
    int start=0;int step=(1<<30);
    for(;step;step>>=1)
    {
        int index=start+step;
        if(zerouri(index)<=val) start=index;
    }return start;
}
int main()
{
        freopen("fact.in","r",stdin);
        freopen("fact.out","w",stdout);
    scanf("%d",&p);
    int val=cautbin(p);
    printf("%d",val-val%5);
}