#include <stdio.h>
#include <stdint.h>
uint16_t binary_to_uint(const char *str) {
// Your logic here
uint16_t num = 0;
while(*str != '\0'){
num = num << 1; //multiply by 2
if(*str == '1'){
num += 1; ////add 1 iff bit is 1
} else if(*str != '0'){
return 0; ///return 0 if find invalid char
}
str++;
}
return num;
}
int main() {
char bin[20];
scanf("%s", bin);
printf("%u", binary_to_uint(bin));
return 0;
}