#include<stdio.h>
#define LL long long
int main()
{
LL n,ans;
while(scanf("%lld",&n)!=EOF)
{
ans=0;
while(n)
{
ans+=n/5;
n/=5;
}
printf("%lld
",ans);
}
}
#include<stdio.h>
#define LL long long
int main()
{
LL n,ans;
while(scanf("%lld",&n)!=EOF)
{
ans=0;
while(n)
{
ans+=n/5;
n/=5;
}
printf("%lld
",ans);
}
}