2747: 期末考试来啦!
#include<stdio.h>
typedef long long LL;
bool check(LL x,int n)
{
LL sum=0,t=5;
while(t<=x)
{
sum+=x/t;
t*=5;
}
return sum>=n;
}
int main()
{
int n;scanf("%d",&n);
LL l=0,r=1e18;
while(l<r)
{
LL mid=(l+r)/2;
if(check(mid,n)) r=mid;
else l=mid+1;
}
printf("%lld\n",l);
return 0;
}