#include <iostream>
#include <stdio.h>
using namespace std;
FILE *f,*g;
long long v[123]={25,125,625,3125,15625,78125,390625,1953125,9765625,48828125,244140625};
int main()
{
    long long p,i,k=0,c=0;
    f=fopen("fact.in","r");
    g=fopen("fact.out","w");
    fscanf(f,"%lld",&p);
    p=p*5;
    for(i=1;i<=12;i++)
    {
        if(v[i]>p)
            break;
        else
            c=1;
    }
    if(c==1)
    p-=i*5;
    fprintf(g,"%lld",p);



    fclose(f);
    fclose(g);
    return 0;
}