Extract Even Bits Only from 32-bit Register

#include <stdio.h>
#include <stdint.h>

uint32_t extract_even_bits(uint32_t reg) {
    uint16_t mask = 0, i = 0;
    for (i = 0; i < 16; i++) {
        mask |= ((reg >> 2*i) & 1) << i; // need to shift to position i as well by the last term
    }
    return mask;
}

int main() {
    uint32_t reg;
    scanf("%u", &reg);
    printf("%u", extract_even_bits(reg));
    return 0;
}