#include <stdio.h>
int main() {
    double a, t;
    t = 2;
    scanf("%lf", &a);
    while (a >= 2) {
        t = t * 2;
        a = -;
    }
    printf("%.0lf", t - 1);
    return 0;
}

/sandbox/1/a.c:10:12: error: expected expression
        a=-;
           ^
1 error generated.