#import <stdio.h>
int main() {
    int n;
    scanf("%d ", &n);
    char A[101];
    char B[101];
    char C[101];
    scanf("%s", A);
    scanf("%s", B);
    scanf("%s", C);
    int ans = 0;
    for (int i = 0; i < n; i++) {
        char a = A[i];
        char b = B[i];
        char c = C[i];
        if (a != b && b != c && c != a) ans += 2;
        else if (!(a==b && b==c))
            ans++;
    }
    printf("%d\n", ans);
}
