#include <stdio.h>

int main(void){
    int n; scanf("%d\n", &n);
    int res = 0, one = 0, nine = 0;
    for(int i = 0; i < n; ++i){
        switch(getchar()){
            case '1':
                one++;
                break;
            case '3':
            case '5':
            case '7':
                res++;
                break;
            case '9':
                if(one >= 1){one--; res++;}
                else nine++;
                break;
        }
    }
    int d = (one > nine / 2) ? nine / 2 : one;
    res += d; one -= d;
    res += one / 2;
    printf("%d\n", res);
    
    return 0;
}