输入一个n,求小于n只有1和0组成的数的个数
#include<cstdio>
#include<cmath>
#include<cstring>
#include<iostream>
#include<algorithm>
using namespace std;
#define INF 0x3f3f3f3f
typedef long long ll;
const double eps=1e-8;
int sgn(double a){return a<-eps?-1:a<eps?0:1;}
int main()
{
char s[11];scanf("%s",s);
int len=strlen(s);
int ans=0;
for(int i=0;i<len;i++)
{
if(s[i]>'1')
{
ans+=(1<<(len-i))-1;
break;
}
if(s[i]=='1')
ans+=(1<<(len-i-1));
}
printf("%d",ans);
}