#include <stdio.h>

int main() {
	int data[10] = {1, 3, 5, 7, 9, 11, 13, 15, 17, 19};
	int num = 7;
	int low,high,mid;
	low = 0;
	high = 9;
    
    while(low <= high){
        mid = (low + high) / 2;
        if(num == data[mid]){
            printf("%d ",mid);
            return 0;
        }
    
    else if(num > data[mid]){
        low = mid + 1;
    }
    else if(num < data[mid]){
        high = mid - 1;
    }
    }
    
	return 0;
}